This is another of those super simple LaunchBar features that, it seems, most people don’t know exists. Once you invoke LaunchBar, if you start your command with a number and a mathematical operator, LaunchBar will do the math. For example, if you punch in “2+2”, LaunchBar will present “4” without any further input.
If you press
return, the equation will disappear from the input bar and just the result will show there; if you then start typing an operator, the “saved” result acts as the first operand.