I started yoghurt making using the traditional finger method mentioned in all Middle-eastern books: dip your finger in and if it can stay 15 seconds before starting to burn it's ready, then keeping it somewhere warm for 8-10 hours. I had mixed success with this, failing about 40% of the time because it was very watery.
Upon buying a thermometer, I mix in the culture at 49 degrees C (120 F). This is far cooler than the finger method, which my thermometer reads as around 60+ degrees C (140+ F). But I get great results each time.
Do you use a thermometer or the finger method for making yoghurt?