I recommend using the freshest spices possible to make a tincture with cheap vodka. Add 10 cinnamon sticks, 1/2 of a freshly grated nutmed seed and two crushed cloves to a pint jar filled with vodka. Let it sit for a week in the cupboard, giving it a good shake once a day. Add the (very strong) infusion 1 tsp at a time to the mead, giving it a gentle swirl after each addition. Taste the mead and decide once the spice level is perfect for your tastes. There is no other way to precisely dose spices. It works perfect with beer, too.
"Good people drink good beer." -HST