Q. What is the difference between the RT-21 and the RT-21D?

A. The RT-21D has a high readability Vacuum Fluorescent Display.  This display is bright blue in color and can be easily used in bright outdoor sunlit locations.  For aesthetic reasons, the VFD looks great against a black panel, so the ‘D’ version also incorporates a matte finish black Lexan overlay in place of the cream color in the standard unit.

There are no functional differences between the two controllers.  If you click here you can see the actual units.

Q. What is NEW about the RT-21 over the previous model RT-20?

A. Click here for RT-21 New Features.