I use one scale and measure the back and front separatly, putting the wheels I do not measure on something that is equal height to the scale (3 racing car stand happen to be the same height as my scale..), and make sure I put the wheels on the same spots when I turn it around. For side to side I use the Hudy tool but there is better ways I think.
Lastly I use the Hudy tweak board, it is great!

The front / back and side to side you only need to do if you rebuild smth that may affect the weight balance of the car, tweak you should check all the time.