Calibrate Your Tun (using weight and material)
This method is less accurate than the above method but will give you a ballpark figure to use in the mash calculations.
Calibrate Your Tun (using hot water)
Use this to calculate strike water temperature and volume to obtain the correct target temperature of a single infusion mash. Add a volume of water close to your mash amount at a similar temperature. Measure the temperature after 0, 5, and 65 minutes.