How can you tell which level of reading glasses are needed based on prescription numbers?

Needs testing: The closer you want to hold your reading material the higher the number needs to be but it does give you more magnification. Ont he other hand if you want to look at the computer screen which is generally further back you need a weaker lens such as perhaps +1.00.

Age-related: You are in your 30's, usually people your age don't need readers, so you may want to see an eye doctor. 42-47 year olds usually need +1.25 to 1.50, with increases of .25 every few years more info about it: http://www.2020vision.Com/monovision.Html.