Hi,

would it be possible to add an information about the positions of the alarm bits used in functions setA1Time and setA2Time please (I don't know how to do it by my self, sorry).

Having a look inside the setA1Time and setA2Time code and the DS3231.pdf, the use of AlarmBits parameter is not obvious.

Could you specify something like this, whatever the function setA1Time or setA2Time used, the AlarmBits parameter bits are placed this way (b7 to b0) :
x A2M4 A2M3 A2M2 A1M4 A1M3 A1M2 A1M1

Those bits correspond to page12/20 of DS3231.pdf from www.maximintegrated.com file.

Thanks.

Sometimes I feel really stupid, like right now.. sorry, but I need to ask:
You write a lot of possible functions, but I can't find any description..?
I know I can open the examples and can find several functions but not all and not ordered.

Battery powered RTC seems to be frozen after Arduino power up. The command RTC.now() is reporting 165:165:85 which does not make any sense. As the device is powered and battery is soldered, I am unable to cut its power.

Proposed solution: the class should provide a mechanism to control manually the logic level of the output digital pins to attempt to unlock the communication channel, e.g. the i2c bus is always "busy".

The documentation indicates to use Unix time.
Trying to set DS3231 RTC using setEpoch() function gives wrong dates.
Substracting 946684800ul (30 years) from 'epoch' parameter solves the issue.

This is not really an issue, so please close, when read!

Hi everyone, Hi @awickert,

I took the liberty and added a changlog to the master branch to keep track of changes, additions, etc, that go into future versions. With more people contributing, I hope to keep track of more recent changes.

The structure is rather simple: The changelog consists of a list of sections, one per version, latest first. Above the latest version section, there is a section for the next, upcoming version. Whenever there is an addition of a feature or a change in code (either through direct edits or through PRs), add the changes as a bullet point to the upcoming versions sections.

When ready for the next version, change the upcoming version section to the next build-version and introduce a new upcoming version.

Final note on the bullet points: Be precise and comprehensive, just like in your commit messages.

Best regards,
Jacob

There does not appear to be any documentation for this library anywhere, which isn't great. There are examples, but that doesn't tell anyone what the function signatures are, what input they expect, and what output they yield. Can that be added? Also, as a splice of the Adafruit library, where are the initialized and adjust functions? Because those are incredibly useful =)

(being able to say rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); makes setting the RTC entirely trivial compared to having to call seven separate functions)

Not sure it is a bug.
i'm unable to compile "DS3231_set" example

error message
DS3231_set:13:8: error: 'DS3231 clock' redeclared as different kind of symbol
DS3231 clock;

Arduino uno R3
latest ide 1.8.19
win 7
DS3131 version 1.1.0

Hey, I use this library and wehen I set the time of the RTC ds3231 to the current time (UTC time zone) and afterwards ask for timestamp.hour()(minute()/seconds() and the unixtime() the unix time is offset compared to hours, minutes by 2 hours
can it be that the ds3231 can be set to a specific time zone and thereby gives me this offset?
thanks

Could the following method be vulnerable to the Year 2106 Problem, since it returns an unsigned int?
uint32_t unixtime(void) const;

Plus, I think for a unix timestamp, it should be given as an unsigned long.

If the arduino boots up and the RTC is not connected, it will not return error values for some parameters such as date and time.

A simple fix is to add the following lines of code in every method:

if (!Wire.available())
{
    return 99; // Some obvious error value
}

For example in the getSecond() method:

byte DS3231::getSecond() {
    Wire.beginTransmission(CLOCK_ADDRESS);
    Wire.write(0x00);
    Wire.endTransmission();
    Wire.requestFrom(CLOCK_ADDRESS, 1);

        if (!Wire.available())
        {
            return 99; // Some obvious error value
        }

    return bcdToDec(Wire.read());
}

Hi,
I am trying to load this example Arduino on a Nano attached to a DS3231 RTC and it fails with these error messages. Is there an update available?

Using library DS3231 at version 1.1.0 in folder: S:\MyProject\AVR\Arduinosketchbook\libraries\DS3231
Using library Wire at version 1.0 in folder:
\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.5\libraries\Wire
exit status 1
'DS3231 clock' redeclared as different kind of symbol

Posting an issue here that I am working to understand and resolve.

Recent PRs added overloads to the functions for getAXAlarm() and checkIfAlarm().

I am encountering fatal errors during compilation of the library's .cpp file with these overloads. The compiler seems to fail to find the second, overloading prototype in the header file.

For example:

error: prototype for 'void DS3231::getA1Time(byte&, byte&, byte&, byte&, byte&, bool&, bool&, bool&, bool)' does not match any in class 'DS3231'
void DS3231::getA1Time(byte& A1Day, byte& A1Hour, byte& A1Minute, byte& A1Second, byte& AlarmBits, bool& A1Dy, bool& A1h12, bool& A1PM, bool clearAlarmBits) {
^~~~~~
error: candidate is: void DS3231::getA1Time(byte&, byte&, byte&, byte&, byte&, bool&, bool&, bool&)
void DS3231::getA1Time(byte& A1Day, byte& A1Hour, byte& A1Minute, byte& A1Second, byte& AlarmBits, bool& A1Dy, bool& A1h12, bool& A1PM) {
^~~~~~

I saw, that getA1Time and getA2Time do not clear parameter AlarmBits before setting certain bits there.
Probably they were written this way to facilitate combining the AlarmBits of these two functions when called in sequence.

Please add a note in DS3231.h, that variable AlarmBits needs to be cleared before calling getA1/2Time to avoid 'random' output.
Also clear that variable in DS3231_test.pde.
This may be a reason for issue #7 (Alarm 2 gives wrong Alarm bits back).

If combining the AlarmBits of A1 and A2 is not so important for you, you may want to change the first assignment of AlarmBits in getA1Time/getA2Time from
AlarmBits = AlarmBits | (temp_buffer & ...
to
AlarmBits = (temp_buffer & ...

when i try to run examples/now/now.pde on my Seeeduino XIAO, i get the following error:

In file included from /Users/tlossen/Library/Arduino15/packages/Seeeduino/tools/CMSIS-Atmel/1.2.1/CMSIS-Atmel/CMSIS/Device/ATMEL/samd21/include/samd21.h:69:0,
                 from /Users/tlossen/Library/Arduino15/packages/Seeeduino/tools/CMSIS-Atmel/1.2.1/CMSIS-Atmel/CMSIS/Device/ATMEL/samd.h:105,
                 from /Users/tlossen/Library/Arduino15/packages/Seeeduino/tools/CMSIS-Atmel/1.2.1/CMSIS-Atmel/CMSIS/Device/ATMEL/sam.h:540,
                 from /Users/tlossen/Library/Arduino15/packages/Seeeduino/hardware/samd/1.8.1/cores/arduino/Arduino.h:49,
                 from sketch/rtc_now.ino.cpp:1:
/Users/tlossen/Library/Arduino15/packages/Seeeduino/tools/CMSIS-Atmel/1.2.1/CMSIS-Atmel/CMSIS/Device/ATMEL/samd21/include/samd21g18a.h:476:27: error: expected ',' or '...' before '(' token
 #define PM                ((Pm       *)0x40000400UL) /**< \brief (PM) APB Base Address */
                           ^
/Users/tlossen/Documents/Arduino/libraries/DS3231/DS3231.h:71:33: note: in expansion of macro 'PM'
   byte getHour(bool& h12, bool& PM);
                                 ^~
exit status 1
Error compiling for board Seeeduino XIAO.

it seems that the variable PM clashes with a macro defined for samd21 boards?

The following constructor caused a hard fault on a SAMD21 device:

DateTime (const char* date, const char* time);

The following minimal snippet illustrates the trouble:

#include <DS3231.h>
DateTime trouble("Jan 12 2023", "12:07:00");
void setup() {
  ;
}
void loop() {
  ;
}

Immediately after uploading, the device loses its Serial connection to the computer. The connection must be restored with a quick double-tap of the reset button before code can be uploaded again.

The other constructors, that use numeric parameters, do not cause this problem in a declaration statement. However, I might have seen a similar result when using the RTClib::now() function farther along in a program. Can't remember.

Perhaps DateTime should be approached with caution on SAMD21 hardware because this repo was written for 8-bit AVR chips. I wonder whether an attempt to read or write some memory location that is not 32-bit aligned may be causing a hard fault which hangs up the CPU.

In the interest of preserving compactness when compiled for AVRs, it may be desirable to create an alternate code body for DateTime to be compiled for the SAMD21G18A architecture. Putting this issue out there for the community to consider. Hope someone who knows the DateTime code intimately can address this issue with skill, before I try to wrap my amateurish hands around it.

David

Current the OSF flag is reset in setSeconds() and no other function is provided to do it. This seems like a bit of an arbitrary choice and has led to some unpredictable errors occurring for me where this flag was being reset without me knowing how. The documentation says it makes good housekeeping sense and perhaps that's true but surely that should the user should at least be given the choice?

I propose that:

1. Clear OSF flag functionality should be removed from setSeconds().
2. Clear OSF flag function be defined independently to perform this role.

Hi,

I discovered that Alarm 2 gives wrong alarm bits back when reading them. I'm not sure if the wrong bits are written to the controller or if just the reading is wrong. but I think its a combination of both problems.
Alarm 1 works totally fine

I checked the docs, the examples, the header, and the cpp file, and can find no mention of whether this library counts Monday or Sunday as doW 1. (Yes some people consider the week to start on Sunday while others consider it to start on Monday)

Does it matter? I don't know, but I can't find anything that says anything.

The datasheet link in the About the DS3231 section is broken.

The version value in library.properties was not updated before creating the 1.0.3 release of the library:
https://github.com/NorthernWidget/DS3231/blob/v1.0.3/library.properties#L2
That caused 1.0.3 to not get picked up by the Arduino Library Manager indexer job.

This means that anyone installing the library via Library Manager is getting an outdated version of the library.

First time using github, so apologies if this isn't in the format you'd expect; happy to take advice on improvements as necessary!

I've been trying to use the DS3231 Arduino library and decided to make a start with the "echo_time" example file as I believe my module still has a time inside it from when I used it some time ago. Upon doing so, I discovered that the example file cannot compile due to several errors, as follows:

• Line 33: 'Century' is not declared in scope
• Line 37: 'h12' is not declared in scope
• Line 37: 'PM' is not declared in scope
• Line 41/42: Missing '}' at the end of the for loop. Actual compile error points to line 44, but this is the cause.

For my general understanding of how these functions work, should the three variables simply need to be declared (as globals?) and 'passed' (as a pointer?) to the respective functions which will then change their value? Apologies if that's not the correct terminology!

Hope this helps.
Oli

Code using the DS3231 library was working until the library was updated. Is there something missing in nanf("")?

Arduino: 1.8.13 (Linux), Board: "Arduino Uno"

/home/kraig/Arduino/libraries/DS3231/DS3231.cpp: In member function 'float DS3231::getTemperature()':
/home/kraig/Arduino/libraries/DS3231/DS3231.cpp:414:16: error: 'nanf' was not declared in this scope; did you mean 'tanf'?
414 | temp3231 = nanf(""); // Not a number
| ^~~~
| tanf
exit status 1
Error compiling for board Arduino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

Hi,

I miss a new release, can you make one?

I can not see the version 1.1.1 in Arduino library description:

• https://www.arduino.cc/reference/en/libraries/ds3231/

And also (probably because of that) I can not install it with arduino-cli - it installs version 1.1.0:

$ arduino-cli lib install DS3231
Downloading [email protected]...
[email protected] already downloaded
Installing [email protected]...
Installed [email protected]

While comparing version 1.1.0 and 1.1.1 I see that library.properties were not updated, but not sure what else is needed to make new version of this library. See also: #64 (comment).

I know that I can install the library by ZIP or GIT reference but it would be good if the newest version could be installed by Arduino IDE Library Manager:

Hello,
tried to compile a sketch for MKRFOX1200 and got this error:
/Users/xxx/Documents/Arduino/libraries/DS3231-master/DS3231.cpp: In constructor 'DateTime::DateTime(const char*, const char*)'
/Users/xxx/Documents/Arduino/libraries/DS3231-master/DS3231.cpp:130:22: error: uninitialized const 'buff' [-fpermissive] static const char buff[4];

I added the initialization code and everything was fixed, please consider my PR ;)

In that document, under the description of the getYear() function, there's a piece of text as follows:
_/*

• returns: byte = 00 to 99
• parameters: none
• asserts: none
• side effects: none
• DS3231 register addressed: 0x06
  */

byte theDate = myRTC.getDate();_

Which no doubt should have been:

_/*

• returns: byte = 00 to 99
• parameters: none
• asserts: none
• side effects: none
• DS3231 register addressed: 0x06
  */

byte theYear = myRTC.getYear();_

Gerard

Can we get '<', '>', '-', '+' operator overloading for the DateTime class?

I can submit a pull request to implement this if you like.

Hi everybody,

I'm using the DS3231 module and tried to modify the "now" example code:

void loop () {
    
    delay(1000);
    
    DateTime now = myRTC.now();
    
    Serial.print(now.year(), DEC);
    Serial.print('/');
    Serial.print(now.month(), DEC);
    Serial.print('/');
    Serial.print(now.day(), DEC);
    Serial.print(' ');
    Serial.print(now.hour(), DEC);
    Serial.print(':');
    Serial.print(now.minute(), DEC);
    Serial.print(':');
    Serial.print(now.second(), DEC);
    Serial.println();
    
    **Serial.print(now.dayOfTheWeek(), DEC);
    Serial.println();** 

but I got the error message
.../now/now.ino:37: undefined reference to DateTime::dayOfTheWeek() const`

what am I doing wrong? I use Arduno IDE 2.2.1 and DS33231 lib 1.1.2

Thank you
Marc

There always were some minor notifications while compiling but now I get this:
Never mind. The update function "simply" pasted this library over another one i had installed....

I am working with DS3231's alarm programming and there is no documentation. Can someone explain what these parameters mean?

setA1Time(byte A1Day, byte A1Hour, byte A1Minute, byte A1Second, byte AlarmBits, bool A1Dy, bool A1h12, bool A1PM);

Requesting input from C++ experts regarding a puzzling behavior of the DateTime class as defined in this DS3231.h.

In Arduino IDE 1.8.15, at least, the following assignment ("=" operator) compiled and executed without error or any warning related to type mismatch between the LH and RH operands.

#include <DS3231.h>
DateTime myDT;
uint32_t arbitraryInteger = 42;

void setup() {
  myDT = arbitraryInteger;
  // ...moreover, to make it perfectly clear...
  myDT = 42;
}

Meaningless date and time values wwere retrieved from the DateTime instance following such an assignment.

Code writers using this library should exercise care to ensure that only sensible values are assigned to a DateTime instance.

My question for the community is whether -- and how -- the DateTime class can be defined in such a way that the Arduino IDE compiler will reject assignments of values, to a DateTime instance, that are of other, different, incompatible data types.

Arduino: 1.8.17 Hourly Build 2021/09/06 02:34 (Mac OS X), Board: "ATmega2560, Yes (UART0), EEPROM retained, Arduino MEGA pinout, BOD 2.7V, LTO enabled, External 16 MHz"

/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp: In constructor 'DateTime::DateTime(uint32_t)':
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp:104:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if (days < 365 + leap)
~~~~~^~~~~~~~~~~~
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp: In member function 'void DS3231::setEpoch(time_t, bool)':
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp:264:12: error: aggregate 'DS3231::setEpoch(time_t, bool)::tm tmnow' has incomplete type and cannot be defined
struct tm tmnow;
^~~~~
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp:266:3: error: 'localtime_r' was not declared in this scope
localtime_r(&epoch, &tmnow);
^~~~~~~~~~~
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp:269:3: error: 'gmtime_r' was not declared in this scope
gmtime_r(&epoch, &tmnow);
^~~~~~~~
/Users/name/Documents/Arduino/libraries/DS3231/DS3231.cpp:269:3: note: suggested alternative: 'time_t'
gmtime_r(&epoch, &tmnow);
^~~~~~~~
time_t
Mehrere Bibliotheken wurden für "Timezone.h" gefunden
Benutzt: /Users/name/Documents/Arduino/libraries/Timezone
Nicht benutzt: /Users/name/Documents/Arduino/libraries/Timezone-master
Mehrere Bibliotheken wurden für "TimeLib.h" gefunden
Benutzt: /Users/name/Documents/Arduino/libraries/Time-master
Nicht benutzt: /Users/name/Documents/Arduino/libraries/Time
exit status 1
Fehler beim Kompilieren für das Board ATmega2560.

Dieser Bericht wäre detaillierter, wenn die Option
"Ausführliche Ausgabe während der Kompilierung"
in Datei -> Voreinstellungen aktiviert wäre.

My idea is to make a method which has a parameter epoch which sets then the rtc, like time and date, automatically?
How do you think about?

Once alarm is triggered method DS3231::turnOffAlarm(byte Alarm) does not reset A1F / A2F bits in status register 0x0F. This makes SQW pin stay LOW and thus making following interrupts impossible.

Simple solution would be to add following codes at the end of the method to modify status byte as well.

	// clear A1F/A2F flags for previously set alarms
	temp_buffer = readControlByte(1);
	// modify status byte
	if (Alarm == 1) {
		temp_buffer = temp_buffer & 0b11111110;
	} else {
		temp_buffer = temp_buffer & 0b11111101;
	}
	writeControlByte(temp_buffer, 1);

Thanks for the library!

Hi,

Within DS3231.cpp, there is no possibility to update the "century" bit at adress 0x05h, bit 7.
You can read it with getMonth(&century) but using decToBcd(month) in the setMonth(month) routine doesn't allow to write it with for example setMonth( 0x80h OR month ).

A standalone function setCentury(bool Century) could be useful to complete the library :)

Yes... I know... the "century" bit is not very useful ;)

Best regards

Compilation error: 'class DS3231' has no member named 'begin'

Hi Andy,

I introduced a method 'setEpoch' to the DS3231 code.
Now I am thinking about to query the Epoch value back from the Ds3231 to feed the (for example) every hour the ESP8266.

Background is that the ESP8266 has ab very bad time accuracy, and want to feed it every hour by the Epoch queried from the RTC.

Is it possible to get the Epoch from the DS3231?

I encountered a problem when using the checkifalarm function. This function gives some issues, since my arduino code is only checking the alarms constantly and not doing anything else,

In the function the flags are red and then reset to 0, even when the flag isn't 1. This is problematic, since my code is nearly all of the time in the checkifalarm function. First the controlbyte is red out in this function, and the flag can be red as zero. In the meanwhile the flag can be set to 1 by the chip, but the code will still set the flag to zero. So the alarm is never triggered. This can easily be solved by the following code change:

bool DS3231::checkIfAlarm(byte Alarm) {
	// Checks whether alarm 1 or alarm 2 flag is on, returns T/F accordingly.
	// Turns flag off, also.
	// defaults to checking alarm 2, unless Alarm == 1.
	byte result;
	byte temp_buffer = readControlByte(1);
	if (Alarm == 1) {
		// Did alarm 1 go off?
		result = temp_buffer & 0b00000001;
		// clear flag
		if (result == 1)
		{
			temp_buffer = temp_buffer & 0b11111110;
			writeControlByte(temp_buffer, 1);
		}
	} else {
		// Did alarm 2 go off?
		result = temp_buffer & 0b00000010;
		// clear flag
		if (result == 0b10)
		{
			temp_buffer = temp_buffer & 0b11111101;
			writeControlByte(temp_buffer, 1);
		}
	}
	return result;
}

I don't know if this is the right place to put it, I am just new on Github. But please take a close look at it.

There are macros "PM" and "RTC" present. Do not use these as variable names in examples (RTC) and in library (PM). Simply use low-case.

C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp: In constructor 'DateTime::DateTime(const char*, const char*)':
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:132:41: warning: writing into constant object (argument 3) [-Wformat=]
sscanf(date, "%s %d %d", buff, &d, &y);
^
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:132:41: warning: format '%d' expects argument of type 'int*', but argument 4 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:132:41: warning: writing into constant object (argument 3) [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:132:41: warning: format '%d' expects argument of type 'int*', but argument 4 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 3 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
sscanf(time, "%d:%d:%d", &hh, &mm, &ss);
^
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 4 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 5 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 3 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 4 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:135:42: warning: format '%d' expects argument of type 'int*', but argument 5 has type 'uint8_t* {aka unsigned char*}' [-Wformat=]
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp: In member function 'byte DS3231::getMonth(bool&)':
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:244:7: warning: unused variable 'hour' [-Wunused-variable]
byte hour;
^
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp: At global scope:
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:138:16: warning: 'uint8_t conv2d(const char*)' defined but not used [-Wunused-function]
static uint8_t conv2d(const char* p) {
^
C:\Users\admin\Documents\Arduino\libraries\DS3231\DS3231.cpp:158:16: warning: 'uint8_t bin2bcd(uint8_t)' defined but not used [-Wunused-function]
static uint8_t bin2bcd (uint8_t val) { return val + 6 * (val / 10); }
#44

@awickert @IowaDave

Why do we use the yOff instead using the hole year number (e.g. 2023) in the DateTime Class?
Is ist possible to switch to use the year?

I would sugest to switch to

uint16_t year

as Data member for DateTime so no year information is lost.

Or maybee better to add the full year as Data member.
To be able to recalculate timesstanps in a way.

I could provide a solution.

The leap year calculation is currently set to y % 4 == 0. The correct logic to determine a leap year is y % 4 == 0 && (y % 100 > 0 || y % 400 == 0). Every 4 years is a leap year except centuries, unless the year is divisible by 400. I.E. 2000 was a leap year, 1900 and 2100 are not.

@NorthernWidget

PRs for significant issues going back to last July, no response. I emailed the claimed maintainer, [email protected], no response.

Is there anybody out there?

My DS3231 loses a couple of secs/day. Research revealed the existence of an 'AgingRegister'. I'm not a C/C++ programmer, just a continually learning 'Arduino' progarmmer and so far I've not learned how to use it after reading many threads and browsing several DS3231 libraries.

I'd guess many users at a similar skill level would benefit from an Example sketch or independent function that allowed simple adustment of this register. Trial and error could then restore tolerable accuracy.