How to get a Text box condition to change the status of a check box in VBA (ms-word)

I am creating a form that requires the user to input into the text box a number (pressure reading). The form then has a check box that the user checks in order to indicate that the pressure reading is within range. I would like to set the Text box to check the checkbox if an integer inputted into the text box is greater than the specification (50 psi). I am very new to VBA and code in general so I don't even know where to begin.