There is few meaaurement for each brand to rate their stiffness. Some use flex, mid flex, stiff Some use 2/5,3/5,4/5 (1-full flex, 5-extra stiff) some other use 8.0, 8.5, 9.0 Ignoring the fact that each brand have their own stiffness (like most lining is softer than Yonex with the same spec), im kinda confuse to read on the 3rd type (8.0, 8.5, 9.0). Does bigger number mean stiffer or smaller number mean stiffer?
It'd be interesting to see a spreadsheet with test data of various rackets from different brands showing bending stiffnesses of rackets. I guess just measuring the relative displacement to an applied force would give us a stiffness value? But who has time or money to do this
I have explained it before. They use a certain amount of pressure on the shaft and measure deformation in cm. That is why the higher the number the flexier the racket.