In article , Alan alz_deane@nosp
am.ntlworld.com writes
You don't say - is it a solid-state meter, or an old-style with a
rotating disc? If it's disc type, they are moderately easy to check with
a bit of simple arithmetic, the name plate will have a figure for the
number of revolutions per kwh.

Sorry, modern solid-state meter :-(

The principle is exactly the same, measure the exact time between 2
readings ie. start when the smallest digit clicks over & then stop again
when the smallest digit ticks over some (much higher) reading later.

My electronic meter has a 0.01kWhr resolution, so the worst
measurement reading error you can have if measuring over ~1kWhr is 1%
and if you start & stop exactly when the dials (or lcd) clicks over then it will
be better than that.

The load you are using (1kw fire or 3kw fan heater) will certainly not be an
accurate load, just measured one here (1kW) and it was 1088W so 8.8%
error. That will be the limiting factor of your accuracy.

So you should be able to check accuracy within about 10% quite easily
which may suit you as it appears you are looking for gross errors rather
than the last 0.1%.
--
fred