Oven Thermometers

I recently bought Heston Blumenthal's recipe book, his recipes can be a bit involved but the one's I have tried have been worth the effort.  One of his recommended pieces of kit is an oven thermometer which I bought - they aren't expensive and give the true temperature of your oven which I find never agrees with the oven's own thermometer - maybe that's why my Yorkshire Puddings never rise!

http://www.lakeland.co.uk/11235/Oven-Thermometer