if it is just for doing the crown test, you can strap the pen to the vacuum part like shown here. Just strap it down so the pen doesn’t move to much. I did not do this the first time and you can clearly see the result before and after 
if it is just for doing the crown test, you can strap the pen to the vacuum part like shown here. Just strap it down so the pen doesn’t move to much. I did not do this the first time and you can clearly see the result before and after