I have that exact same scale and have been using it trouble free for many years.
Anyway, nothing is broken or other wise malfunctioning. Put the entire scale back together again, except for the bird shot, keep that off to the side for what's next. OK, now adjust the front foot in untl the scale looks fairly level setting on the table, doesn't have to be perfect by any means for this step. Now hang the pan assembly on the back end of the beam where it normally hangs, the complete assembly except for the bird shot. Now turn the .1 grain or tenth grain wheel to absolute zero. Next set/slide the main beam weight to absolute zero. Now start adding bird shot until the pan starts floating pretty close to center line, or just some if it isn't possible to get that close to center with those shot sizes. Once you have it floating start carefully tunring the front foot until the pointer is alligned perfectly with the ceter line, your scale is now zeroed out.
Always use your scale on a fairly flat surface, and if the surface has a lean place the scale so either the pointer or the rear portion of the beam is facing either up or down hill.
How to use it. Every session requires the scale to be zeroed again. This is because once it's been moved it's orientation to level will usually change, and it doesn't take much of a difference to significantly effect accuracy and correct weight. Lets pick a powder charge of 11.3 grains. Turn the wheel until it is at 1.3 grs. and then slide the main weight to the first mark or notch which is 10 grs..
A charge of 6.4 grs.. Zero out the scale of course and then turn the wheel to the 6.4 gr. mark, done.
One more, zero out the scale, 66.8 grs.. Turn the wheel to 6.8 and slide the main weight to the 6th line.
I hope this helped. I remember how it was for me having to learn without the internet or any other easy source for information.
Welcome to THR!