How can I display an insert 1:1 on my monitor?

Make sure that the screen has been calibrated for 1:1 display. You can calibrate the screen in the GP Manager by selecting "GP Admin" -> "Calibrate screen", this is described in the GP Manager manual.

Attention: If you use different monitor models, make sure that you can only calibrate the settings for one monitor. If the monitors are not identical, it is not guaranteed that the 1:1 display is guaranteed on both monitors.