The 35P prints or displays data when I have not shot over it:

The source of “False triggers” can be difficult to identify. Some common causes are:

• Corrosion or oxidation of the Skyscreen plugs: Use a Scotchbrite pad (not steel wool) and rag with rubbing alcohol to lightly polish the plugs. Once they are clean insert them into the chronograph. Gently rotate the plugs back and forth in the jack to further clean/polish the electrical contact area.
• Insufficient light level: The Skyscreens must have open sky above them; they will not work under trees or structures. The orange diffusers are for use under bright/sunny conditions, they should be removed when it is overcast or the sun is low on the horizon.
• Electrical interference: Radar towers, electric fences, air compressors etc. have all been known to produce high levels of electrical noise. These items should be turned off if possible; if not possible the light level entering the Skyscreen sensor should be increased. The quickest way to do so is by removing the Orange Diffusers.

If the 35P is to be used indoors proper incandescent lighting must be used. Oehler Skyscreens will not function under fluorescent lights.