ChangeScale is called automatically when the form that contains the status bar is rescaled. ChangeScale modifies the position as well as the size of a control. Thus, ChangeScale modifies the control's Top, Left, Width, and Height properties. 

The M and D parameters define a fraction by which to scale the control. The M parameter is the multiplier and the D parameter is the divisor. For example, to make a control 75% of its original size, specify the value of M as 75, and the value of D as 100 (75/100). Alternately, the same results are achieved by specifying the value of M as 3, and the value of D as 4 (3/4). Both fractions are equal and result in the control being scaled by the same amount, 75%.  

TCustomStatusBar overrides the inherited method to ensure that the new size of the status bar matches the system font if the UseSystemFont property is true. 

UseSystemFont