1, Find the total finished weight of your top and bottom sashes including glass.

2, For the top sash, add 2 lb to the total, the weights must be heavier than the top sash to ensure the sash stays in place.

3, For the bottom sash, subtract 2lb from the total, the weights must be lighter than the bottom sash to prevent the sash rising.

4, Divide the totals by 2 to find the sash weights required, 2 sashes = 4 sash weights.

Example,

44lb top sash
+2lb balance adjustment
46lb total

23lb 2 weights

44lb bottom sash
-2lb balance adjustment
42lb total