For spaces less than an inch, round down to the nearest 1/8 inch.
Choose the number that matches the first number of your prescription most closely (for example, -2.00), and if necessary, round down rather than up.
For example, if a label states that a food has 18 grams of carbohydrates, you can round down and consider it to contain only one carbohydrate choice.
If your measurement is only a quarter or a half of an inch above an even number, round down to that number (for example, round 38.5 down to 38).
