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I want to check how accurate is a clock on a wp34s calculator I got recently.
For this I set it to a computer clock, which, allegedely, synchronizes with time server every hour or so. And then I recorded date, time and the difference between computer clock and calculator clock every once in a while.

Here is the record:
2013-06-06 12 00 00 +0:01:01 d0
2013-06-07 12 00 00 +0:01:02 d1
2013-06-10 08:00:40 +0:01:06 d4.3333
2013-06-17 09:41:53 +0:01:14 d11.4040856 ~ 1.2"/day
2013-06-18 09:30:25 +0:01:15
2013-06-19 09:26:03 +0:01:17
2013-06-21 16:14:18 +0:01:19
2013-06-25 15:47:40 +0:01:24
2013-07-09 07:55:16 +0:01:40
2013-07-10 11:43:08 +0:01:42 ~0.45143 + 1.19638 * x
2013-07-11 15:57:08 +0:01:43
2013-07-15 14:37:54 +0:01:48
2013-07-16 13:55:11 +0:01:49
2013-07-18 15:30:23 +0:01:52

It seems that the rate of 1.2"/day seems pretty steady, but what do I know?
Is there a procedure that allows to determine the rate which is less laborious than fitting least square line into observations over reasonably long period?
And is there way to tell if rate is not steady other than plotting the data and see visually if the line fits?
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