I really like my hps140. (Nice job again, Velleman!) I found that I needed a graticule or grid on the screen to make rf field measurements. I found that plastic cell phone protector sheets work excellent for this. A sheet for Android can be cut into 3 pieces which will fit perfectly over the hps140 screen. I drew lines with a magic marker on the sheet and I now have a grid on my cool little oscilloscope.
Good idea!