In order to complete my basic equipment for sous vide cooking at low and constant temperature I had to find a digital thermometer with an external probe. Here is my choice: a Mastrad thermometer that I purchased EUR 29 on internet. I was amazed to see how reactive the sensor was. You just have to put it in the water and you can see the temperature moving on the spot and reaching the correct temperature in 1 or 2 seconds. This precision will be necessary when measuring the temperature variation with the different techniques of sous vide cooking.