The oil-free compressor compression ratio is a technical representation of the pressure difference, which means the absolute pressure on the high pressure side divided by the absolute pressure on the low pressure side. The compression ratio must be calculated using absolute pressure values. In order to avoid negative values ​​in the calculated compression ratio, absolute pressure must be used instead of gauge pressure when calculating the pressure ratio. It makes sense to use absolute pressure values ​​to make the compression ratio a positive value.