Can one device be used to calibrate several PCs? Can the PCs then be used at the same time?
Do I need to have the device plugged in during normal use, or once the monitor is calibrated can I disconnect it?
You can calibrate a number of computer/monitor combinations, but only the one that the device is attached to can have the ambient light adjustment. Basically, it will "tweak" the profile according to light conditions which, in theory, keeps the display better calibrated. In practice, I didn't find it to matter that much as long as you kept up with a good recalibration frequency.
Yes. This device is a monitor profiler. You connect it to the computer while it performs measurements and creates a profile describing the monitor. You can then use that profile without the device connected.
You can repeat this at will with any number of monitor and even the same monitor under different conditions.