How to terminate the function that runs every n seconds

[Grant Edwards]

On 2015-01-14, Mark Lawrence <breamoreboy at yahoo.co.uk> wrote:
> On 14/01/2015 16:33, Dave Angel wrote:
>
>> Note that neither Timer nor sleep makes any promises about how
>> accurately it matches the requested time.
>
> Reminds me of working on Telematics S200/300/4000/5000 telecomms kit in 
> the early 90s where the timers were mains based, so a one hour timer 
> would go off at about one hour, 30 seconds.

I don't understand.  Power line frequencies are _very_ accurate and
have been relied upon for timekeeping since the 1930s.  We're talking
a few hundred PPM over a 24 hour period.  A 30 second error over a one
hour period seems _really_ high.

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