If you’re comparing to a measurement you may get by using a 48 inch ruler down the back of the club, there can be a variance. Standing a club up and putting a ruler down the back is one way to do it, but there can be inconsistencies in how we hold each club using that method. The bench top ruler that allows us to have the contact point on each iron based on the actual lie angle and that is the most accurate way to measure, but it will give you a different measurement than the ruler down the back. I have not seen 1/2″ variance, but more like 1/8″ to 1/4″. It’s all relative and doesn’t really matter which method you use as long as you are consistent. I recently built a set and did my down the back and then compared to the table top and was about 1/8″ longer on the table top. If you have a club that you know is the length you want, mark it on the table top ruler and work off of that mark. Doesn’t matter what the actual number is. Again, consistency in how you measure is the key.