Good question. I had an electric cooker with a little light on that went out before we moved.
However, we just moved into a house which has a Rangemaster (with gas ovens) and what I do is just switch it on full gas mark 9 for about 10 minutes then turn it down to what I want and shove the food in.
Seems to work but keep an eye on it and use a meat thermometer if you are cooking joints to make sure thay are hot enough.
You can get a thermometer with a dial that you can read through the oven door that sits on the oven shelf. Good cookware shops have them.
* makedoandmend* - not half as stupid as I felt stood in front of the damn thing trying to get the oven gas to come on and not realising that the time clock has to be set before the oven can be switched on.
Don't feel bad about that ABD - I have a friend who got a new cooker and couldn't get to work for weeks before realising he had to set the clock.
All very understandable except that a few years later he moved and completely forgot about the clock thing. It was only when, weeks after, we met in a pub and he was complaining about the bloody cooker not working since he moved that it dawned on him what had happened.
He was someone very high up in the City - which probably explains the state of the economy at the mo...