How do you tune a mridangam?

A mridangam is tuned by striking the leather straps at the head with a smooth stone, often through a wooden peg placed between the straps. Striking towards the shell raises the pitch; striking from below lowers it. The treble head must sound one pitch all round its edge, checked against a sruti box, pitch pipe or tambura. Because the straps link both heads, one adjustment can shift the other.