Another thing to consider is that some of the newer modern machines with very wide feed dogs can mean the fabric is only going over one of them which can make things wonky. Some machines don't have a changeable stitch plate or a way to adjust the needle to the left or right. Agree with the method bearisgray posted about measuring the finished piece. May have to make practice piece for each project if the fabric/thread combo is different. If I am making something with no points and perfect accuracy won't affect the finished project, I just roll with "close enough", and make sure everything is the same amount of "close enough". A nine patch or similar for example is very forgiving.