Why does my jigsaw have two speed controls?

I've noticed that a lot of top-handle jigsaws have both a variable-speed dial and a variable-speed trigger. Isn't one control enough?
— Carisa Anderson, Newport News, Va.

Think of these dual controls in terms of a car, Carisa: The trigger works as the accelerator, and the dial as the gear. You squeeze the trigger to control the blade speed during a cut, feathering it as needed to follow a line. Manufacturers recognize this as the best way to connect your focus to the blade's cutting action. But just as a gear limits a car to a certain speed range, the variable-speed dial limits the top-end speed for each setting. This allows you to squeeze the trigger fully and not exceed your desired speed.

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