A vacuum value needs its units and pressure reference. Absolute pressure is referenced to a vacuum; gauge pressure is referenced to the local atmosphere. Two instruments can describe the same condition with different numbers when their reference conventions differ.
Read the instrument label
WIKA distinguishes absolute, gauge and differential pressure by their reference points. On a composite process record, preserve the convention used by the actual instrument. A value written only as vacuum or pressure is hard to compare with an instruction that uses another basis.
Record the measurement connection
Identify where the instrument is connected and when the reading was taken. A pump display, a bag connection and a separate monitoring point are not automatically interchangeable records. The gauge reference does not explain pressure differences created by the process layout.
Use the applicable process requirement
If a supplier reports a percentage or a negative value, ask how it is defined before comparing it with an absolute-pressure requirement. Do not choose a universal target from an example diagram. Instrument identification, process stage and the required acceptance basis belong together. A correctly labelled reading still does not establish the quality of the finished laminate.
Further reading: WIKA: absolute, gauge and differential pressure.