Time Measurement

There are two long wooden rods of arbitrary lengths. Each takes an hour
to burn and each burns at its constant rate. Without measuring the
length of the rods, how would you clock exact 45 min provided that you
are given as many matchsticks as you need to burn the wood

Answer:

Light the first log and when it completely burns (30 mins) , burn the second log with both the ends (15 mins)