The formula I tried to use was on pg1-25

E = (P/A)/(

*dl*/

*l*)

where, and I can see this must be wrong because the thickness of the plate is not included in "my" interpretation of the formula

P=(loading mass in Kg x 9.81),

A = (length (between supports) x width of plate, in metres)

*dl*= deflection in metres

*l*- (length (between supports) (original dimension

*l*is stated on the page above formula)

OK , I'm not a genius, but what am I missing?