There are three screws to secure the projector on the frame. When you put it back without moving in the z direction, the chance of error is small. Even if you move the projector up or down, all you need to do is calibrate the size of the projected area. Users will need to make sure that the area is the same after they put the projector back (the area is where the error comes from). If the size is not calibrated well, there will be no harm for the printing quality but the size of your printed model will not be the same as before.