Tapping the 
Enter button tells MoboMath that you have completed writing an expression and would like it recognized. You need to use Enter (or wait for a timeout, if one is set) any time you write characters that MoboMath needs to recognize, either in a new math expression or when adding new ink to an existing expression.
All gestures and editing changes that don't involve new characters – such as dragging something to a new location or crossing something out – take effect immediately and don't require an Enter command.
The Enter gesture is another convenient way to recognize your input.
Write this gesture with a single down and left stroke, away from other ink or text on the display.
If you set a timeout in the Preferences dialog, then after the interval you specify MoboMath will automatically recognize what you've written. If a timeout is set, you can still use the Enter command if you want to speed things along.