I made graphs of simple RC and RL circuits. We were told to mark off at 10% of the rise and 10% away from the max. This gives a delta. We were then supposed to use this information form the graph to calculate tau, and compare it with the theoretical value. I know how to calculate the theoretical value, for RC it's just tau = RC and for RL it's just tau = L/R. But then how do you calculate it from the graph?