The optacon 2 manual describes the switch as follows: 1. Normal/ Inverse Video/ Invert Switch The slide switch located on the left side panel, near the back of the unit has three positions: Normal, Inverse Video, and Invert. It should be set to Normal (setting towards the back of the unit) for normal ink print on a white background. The Invert (setting towards the front of the unit) is used for white print on a dark background or for use with a LED display, such as a calculator or a computer monitor. The Inverse Video setting (the center position) is used for computer monitors with a light background and dark letters. If you don't have a user's manual for the optacon 2, let me know and I'll send a text file. I scanned it a year or two ago. Mary To unsubscribe at any time, just send a message to: optacon-l-request@xxxxxxxxxxxxx with the word "unsubscribe" (without the quotes) in the message subject. Tell your friends about the list. They can subscribe by sending a message to: optacon-l-request@xxxxxxxxxxxxx with the word "subscribe" (without the quotes) in the message subject.