Pls explain Step deviations method derivations

Dear student,
Step Deviation
Sometimes, during the application of the short-cut method for finding the mean, the deviation d, are divisible by a common number ‘h’ .In this case the
$di = xi – A$
is reduced to a great extent as di become
$di / h.$
So the formula of mean by this is :
 
Where
$ui = ( xi – A) / h ; h = class width and N = \Sigma fi$

Regards