It is of great importance that you know the correct amount of total and active coils. Closed and squared ends along with closed and ground ends are closed coils. This means that if you have a total amount of 10 coils, you will have to subtract the two closed coils on the ends and calculate a total of 8 active coils. For double closed ends, there are two closed coils on each end so in this case instead of subtracting two closed coils from the 10 total coils, you will subtract four (4) closed coils to calculate a total of 6 active coils. In case that you have a spring with open ends, all coils are active due to the fact that they all have pitch in between.