When starting establish baseline values and mark them "Initial Reading" (the default). Document changes by pressing the "Add" (+) button to create a new set of values. Use the arrow buttons (<>) to travel through the readings and the delete button (X) to remove a reading.
Use multiple readings to help diagnose, track, and document your work. Significant events can be adding or removing refrigerant, cleaning coils, etc. Be sure you allow enough time for the system to settle down adding refrigerant before drawing any conclusions. You can even use multiple "Checkpoint" readings to see how quickly the system is settling into a steady state.