Thanks Ian for clearing the sizing issue. I buy shirts a lot and I agree some shops give the measurement as lay-on-surface and others use the tailor type of measurement.
Sure, you can use either type but the most important thing is to SPECIFY how you measure the garment so we can derive how the shirt will fit (which btw is the most important factor).
SeiberChest and sleeve measurements don't vary by THAT much. It takes about five seconds to determine what method is being used, so I don't really see the issue here. The method used here is also (by far) the most common type used for casual shirts.
Sure, you can use either type but the most important thing is to SPECIFY how you measure the garment so we can derive how the shirt will fit (which btw is the most important factor).