User Skill Threshold
User skill thresholds represent the complexity of everyday (or not-so-everyday) items. To use these items requires a certain baseline of skill. One can attempt to use such items if one does not meet the required parameters, but it is risky. You must rely on good Variance Dice to meet the threshold, every time you attempt to use the device. If you fail to meet the threshold, or have not chance at all, you can still attempt to use the device, but doing so is putting your life in the hands of the Gods or at least the Gamemaster.
Many common devices have negligible user skill thresholds, but complex or technologically advanced devices, such as vehicles, weapons and other equipment, may have significant user skill thresholds. Every time a character with inadequate skill attempts to use a device with too high a user skill threshold, the Gamemaster can assign any number of possible penalties to the attempted skill use. At minimum the difficulty threshold for the test should be increased, and there should be greater consequences for failure: breaking complex and fragile machinery, jamming a gun or shooting a friend by mistake, and so on. Generally it is a bad idea to mess with things you aren’t qualified to use.