One thing I learned early on is that when the directions ask you to cut your squares at, for example 2 7/8", or 2 3/8", I realised this didnt work for me as my HSTs never came out right.

My method is to cut 2 squares the same size. On one side draw a line diagonally, sew 1/4" on both side of the line then cut in half. I always round up, ie 2 2/8" would be 3", 2 3/8" would 2 1/2" (or sometimes even more) I then would use a quilting ruler (6") to square it up.

Afterwards, the first available ruler for this was a ruler by That Patchwork Place called 6" Bias Square up ruler. You pressed your HSTs open then placed the ruler's diagonal line along the seamline and trim ot the size you want.

After this, Eleanor Burns came up with her square up ruler. Again you cut your squares oversize, sew, cut in half then lay the ruler over the unpressed HSTs, trim, then press open afterwards. This is the method I've used for many years and it's my preferred method.