R134A Oil Checker 2 Pack #5030A

I wanted to check the oil in the ac system of my GMC Sierra because I thought it may need some. This item assured me that my ac compressor is not in need of any oil. It saved me from putting oil in my system that doesn't need any.

I keep getting inaccurate reading with this. As soon as you push down on the low pressure hose to much oil comes out as it is under pressure