[Archive]

Posted By: slacks

You can get a loupe or fixed lens that shows markings when you look through it -- it completely takes away the guesswork.

Or, and this is nicked from Beckett's web site:

There are a handful of tools on the market to quickly judge a card's centering, but the most common method uses a ruler and calculator. It doesn't matter whether you measure in picas, decimals, points or any other scale, as long as you use a very finely marked ruler. Measure both sides of a border, and write the numbers down. Let's say the left side measured 12 and the right side measured 5. Add the numbers together (for a total of 17), and divide either of the first two measurements by this total. In the sample case, 12 divided by 17 equals approximately 0.70. The left-right centering on this card is therefore 70/30.