What I do when the customer requires really consistent accuracy, I ask them to create a rectangular box made of 2mm square wire, then, if needed , add 1 mm dia . prongs 3 mm tall on 1 surface.
I then print their file as is in 1 orientation on the platform.
After printing, We measure all the areas and now we can tell the customer what to adjust in his file so we can grow an item accurately.
It is important that the item stay in the same orientation on the platform.
Also, this works only when you use the exact same solution ... If you change solutions, then you have to redo all your calculations.