When is the chip pan at the right temperature?

It's nice if you have the space in your kitchen for a deep fat fryer but if like me space is at a premium you have to make do with a good old-fashioned chip pan. The biggest problem with a chip pan is that you have no way of controlling the temperature accurately and the most difficult part is making sure the fat has reached the right temperature to start cooking.

You often see the tip of using a piece of dry bread to test whether fat has reached the right temperature - when the fat is hot enough the bread will be bubbling on the surface. I have never bothered with this trick as so often what I'm cooking in a chip pan is already frozen. So my tip for checking that the fat has reached the right temperature is to buy a pack of cheap frozen potato wedges and add one of those to the pan. Once it starts to bubble and then rises to the surface you know your chip fat is hot enough.