I am using a delta printer I built and I am having issues with

I am using a delta printer I built and I am having issues with scaling… The x and y length of a phone case I printed should be 65mm and 130mm. It ended up as 67 mm and 134mm. Both divide out to be at a scale of 1.03 compared to the designed dimensions. What causes this? How can I fix it besides just scaling everything down to 97%?

Change DELTA_DIAGONAL_ROD value. Should do the trick.

@Beerend_Groot how much should I change it?