You can use either a traditional glass or digital thermometer, but use the same thermometer throughout your cycle. If you use a traditional glass thermometer always shake it down and make sure you wait for 5 minutes before you read the temperature. If you use a digital thermometer, wait for the beep (usually about 1 minute) before you read and that the temperature will register to 1/10 of a degree. For example: will read 36.56 and not round up to 36.6.
Temps should range from the mid 35's to 37.00. You will not be able to work out anything from one temp alone - You need to temp every morning to be able to understand your temperature shifts.
Hope this helps