Oven temperature

[EEZABLADE32]

Something i've noticed over the years. When checking my oven temperatures with an oven thermometer it does not reach the heat as per the dial, sometimes 10/20 degrees less. I've tried on various ovens and with different thermometers.
Is this normal or am I cursed

[MissNoway.]

When you open the oven door to check the temp will fall.

[heathfield]

I had a Homark oven that from new heated to 30�C higher than indicated by the control knob. It reduced to a blackened lump my first attempt at heating a steak pie. I did as Eezablade did, and used an oven shelf thermometer ever afterwards.