The VBA code to do this is fairly straghtforward, however the data will not be retained in any way, so as soon as the Caibration form closes it will be lost.
The simplest way to do this is to have the VBA code in the Calibration form's On Open event, otherwise you have to refer to the Calibration form in the code.
In the Form's on open event it would be
me.txtPreTestWt1 = 1
me.txtPreTestWt2 = 5
me.txtPreTestWt3 = 10
me.txtPreTestWt4 = 20

For the code in the button it is
Forms!Calibration.txtPreTestWt1 = 1
Forms!Calibration.txtPreTestWt2 = 5
Forms!Calibration.txtPreTestWt3 = 10
Forms!Calibration.txtPreTestWt4 = 20