Use a tape measure diagonally across the top of the frame. Note the inches. Move to the other side, and if the numbers are the same, it's square. secure it with a conner block. If not, tap or move until your numbers match. Secure it when you get it square.
To verify if the frame is flat, use two pieces of string diagonally to each of the corners. If the strings just touch, the table leg heights are correct. If not, you need to adjust the height by moving the frame up or down the legs until the strings just touch. ............. Jerry (in Tucson)
To verify if the frame is flat, use two pieces of string diagonally to each of the corners. If the strings just touch, the table leg heights are correct. If not, you need to adjust the height by moving the frame up or down the legs until the strings just touch. ............. Jerry (in Tucson)