Just how accurate are the low cost free-standing oven thermometers which are sold by many manufacturers such as CDN and Thermaworks?

What do the stove companies use to calibrate their ovens in manufacture or in a service call at your home?

Rose says the accuracy of inexpensive freestanding oven thermometers can be far off the mark. 

My CDN works well and is accurate in that I generally have good results with it.  But it has to be placed exactly where the pan will be, as my oven reads different temps in different places.  I find this thermometer very helpful when i need to bake in someone else’s oven.

Julie, that is exactly what I would have said