Measure vacuum pressure at pump inlet with thermocouple or McLeod Gauge vacuum gauge.
     1. If you do not have a good gauge borrow or buy one.
     2. Check inlet port for cracks in seal or reset NW fitting and clamp.
          A. Inspect O'ring on NW centering ring for cuts wear.
     3. Turn pump on and wait 15 -20 minutes 1 hour is even better.
          A. Read pressure on gauge.  Compare with stated pressure of pump.  Gauge limitations and ambiguities understood.  A good 2 stage pump should show less than .001 micron on untrapped McLeod and 5-7 micron ofr better on thermocouple gauge.  HyVac single stage pumps are 10 to 40 micron higher respectively.
     4. Write down pressure reading of pump.  This is what the pump is    capable of vacuum pressure wise.
     5. Your system should be added and checked piece by piece.
     6.  Pressure attained at the pump inlet is what you are capable of attaining on your system.  Anything less is a leak.  Increasing the size of system expands the time to get to "ultimate pressure" that you have written down.

Vacuum Unit Conversion Chart