IITC defines, IITC has given tolerance limits on model scale and that is ITTC 78, I think, and one can see the IITC proceedings to know exactly what is the model tolerances recommended by a combined body of all tanks. One point I must mention here is that if you have a larger model, then your tolerances can be better than if you have a smaller model. Let us say, whatever be the material of the model you can reach only a certain level of accuracy say for example, you are generating a surface, that surface can be plus minus 1 millimeter of exact nature, now if you have a 2 meter model, then you have that same plus minus 1 millimeter tolerance, and if you have a 5 meter model you again have plus minus 1 millimeter on tolerance- you can understand that the accuracy level for a larger model increases, so if you want very accurate results it is preferable to go for a larger model.