We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "The Medway Handyman"
saying something like:

What's the +/- tolerance on a bog standard wall thermostat?

I mean, if you set it to 20c will it trigger on at 19c & off at 21c?

Do you mean accuracy? I'd be surprised if most domestic stats are any
tighter than +/- 5% of indicated figure, and 10% on older ones.