Weights for the top window:

Add 1KG to the weight
of the top sash window


Divide the total by
2


The result is the
weight of each of the 2 sash weights that you will
require for the top window

Weights for the bottom
window:

Subtract 1KG from the weight of the bottom sash window


Divide the total
by 2


The
result is the weight of each of the 2 sash weights that
you will require for the bottom window 
