Proper Interpretation of Clock Accuracy Spec.

[frostheave]

I am trying to figure out the accuracy of the clock with the following specs:

Arduino Accurate Clock Shield
Clock uses the DS3231 IC from Maxim
Standardized and stackable shield board compatible with the Arduino I/O Pins. Uses the Tx & Rx pins on the controller. Uses I2Cfor host communications <25MHz.
Power: 3-5VDC/ 200uA active, 900nA(timekeep)
Accuracy: 2ppm 0C-40C (~1min/Yr)
L: 2-5/16” W: 1-13/16” WT: .04

The stated accuracy is 2ppm.  Here are my calcs:

* 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 31,536,000 sec/yr
* 31,536,000 sec/yr  /  2,000,000 = 15.768 sec/yr

So, if my math is correct, does this mean the clock is accurate to +- 15.768 sec/yr ?

Thanks for your help!

[jolshefsky]

Accuracy: 2ppm 0C-40C (~1min/Yr)

(...)

* 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 31,536,000 sec/yr
* 31,536,000 sec/yr  /  2,000,000 = 15.768 sec/yr

I think it's 31,536,000 sec/yr * 2 parts/1E6 = 63 sec/yr = ~1min/yr

As for whether that's the correct way of interpreting the data ... I don't know either.

[frostheave]

Accuracy: 2ppm 0C-40C (~1min/Yr)

(...)

* 60 sec/min x 60 min/hr x 24 hr/day x 365 days/yr = 31,536,000 sec/yr
* 31,536,000 sec/yr  /  2,000,000 = 15.768 sec/yr

I think it's 31,536,000 sec/yr * 2 parts/1E6 = 63 sec/yr = ~1min/yr

As for whether that's the correct way of interpreting the data ... I don't know either.

Ah, thank-you jolshefsky.  That makes more sense and it matches the given quote.  I suppose that means
+ or - 63 seconds per year?

[Rick Law]

+ or - up to 63 seconds.

Up to 63 seconds means any numbers <= that 63 magic number.  So it could be off just 1 second, 10 seconds, 62 seconds, or any number from 0-63 seconds.

[frostheave]

+ or - up to 63 seconds.

Up to 63 seconds means any numbers <= that 63 magic number.  So it could be off just 1 second, 10 seconds, 62 seconds, or any number from 0-63 seconds.

Excellent.  Thank-you Rick.