For example, consider the following two scenarios for the hotkey (let's say ctrl+b):
1) Trader has no open positions and decides to open a new long position of 100 shares, so they hit 'ctrl+b' to accomplish that.
2) Trader has an open short position of -600 shares and decides to cover the short position and go flat, so they hit 'ctrl+b' to accomplish that.
Both scenarios used the exact same hotkey, but the share amount the hotkey executed was X=100 to initiate or increase a long position, and X="total short position size" to cover a short position.