We have a use case for the input uom group using parameters and formula. 

I case you are selling wood board, the idea is to use length and width as parameter to calculate the surface (M2) .

I have defined the item in inventory / sales uom : M2. and a input uom group.

in the input uom group , make the conversion between PCS and M2 using 2 parameters to enter on customer order line : width and length. 

on the CO : use the input uom and input qty  : i.e 10 PCS 

the system popup the imput parameter ,  i.e 2.4 m Length and 0.5 width. 

Calculation ==> 1.2 m2 

when updating the CO line, we get : 

input uom PCS , input qty  1.2 (change from initial entry of 10 pcs) why ?? 

sales uom M2 , sales qty  1.2  do not consider the initial input qty of 10 

expected result : 

input uom PCS , qty 10 (should remain unchanged)

sales uom M2, sales qty 12  (1.2 x 10)

thanks for your help