According to the Lord Lyon's specs,

1. The Saltire Flag shall be of undetermined dimensions, but maintaining a 4:5 ratio




2. In order to draw the Saint Andrew's cross, the vertical side of the flag is divided in 6 equal spaces




3. Then a square of the dimensions taken on step 2 is placed on each corner




4. Connect the corners of each square in order to draw the cross




4. And the result is a correctly drawn Saltire Flag





The color is specified as Pantone 300