The huey display calibrator is not designed to calibrate multiple monitors attached to the same computer. If you have dual monitors and your video card supports multiple monitor calibrations, you should check out the higher-end display calibrators such as the i1 Display 2 or i1 Display LT.

If you have two monitors connected to your computer, huey calibrates the monitor that has been designated as the primary monitor. (The primary monitor is the one with the task bar. Monitor designation is done in the Mac System Preferences > Displays > Arrangement or Windows Control Panel > Displays > Settings.)

You may be able to calibrate both monitors if you first designate one as the primary, calibrate it, then designate the second as the primary, and calibrate that. However, this is not a supported feature and may not work with all video cards and monitors. The software for i1 Display, on the other hand, lets you move the display calibration interface to whichever monitor you want to calibrate.