The shear stiffness of a beam in bending is commonly determined by measuring the central deflection δ in a three-point loading test for a range of values of the span L under a constant central load. The value of bending stiffness, EI, and shear stiffness, GA, can then be obtained by plotting δ/L against L2 and drawing the best straight line through the points so obtained. The slope of this line for unit central load is then 1/48EI and its intercept on the δ/L axis is 1/4GA on the simple “Engineer's” theory.