If you are using mast heigth and the formula provided (Mast/nš of marks x 1000) then you need to multiply the result by 4
The thing is, the more I use it the more I realize why real life commanders almost always made simply guesstimates. Once you get the hang of it, it's the easiest way to go

the reticles and such are just a guide. Nothing replaces -or even works better than- the good old seaman's eye.