I have been trying to use an axial extensometer on instron 5560. The data that I get from using the extensometer shows as "strain 1%" is 20 times more than the actual data that I expect ( the data from crossheads moving which is "tensile strain"). How can I change that? The gauge length of extensometer is 1 inch. The gauge length of the crossheads is about 1.5-2 inches.