I did a crappy job of explaining it but please try my method to set all four post complete and absolutely square.
BEFORE you screw anything down just cut 4 battens (thin strips) out of anything scrap laying around that are a little longer than your sides. Clamp/tape all four together. Center punch the centers of your desire post and drill with a appropriate post diameter bit through ALL four pattern strips at once. They are now all SPOT ON for X and Y distance.
Drop them over all four post not yet screwed to your table but loose to slide and shuffle about but they are an exact size but not yet square.
THEN cut two more but these are your EXACT diagonals. Only one is required but with two criss crossed they assure no error and make it really rock solid.
Then slide it around the table where you want and when happy shoot in the base screws.
This sounds so complex perhaps but I can make these battens in less the 20 minutes but the swing is being dead nots square and you can to that is 5 minutes. Then take off the battens and store them for later if you ever need to remount your Primo on a new table.
I wish I can explain how simple it as spotting center points and drilling can’t get easier.
I have TONS of 3 ply baltic birch and would be happy so cobble some up and UPS if anyone domestically wants to try.
-Craig