These are master manometers which used to calibrate the low pressure/Differential pressure instruments. They are battery operated and is suitable for air application only. Model APCAL 5000 has 4½ digit display and one unit i.e. mmwc whereas in APCAL 5100 has 4½ digit display work in NiCD battery and having selectable units. The accuracy of APCAL 500 series is ±0.25% FSD. And APCAL 5100 is ±0.15%. They are available upto 100 psi and maximum static pressure is 100 psi for 5100 and 2000 mmWC for 5100 and 2000 mmWC for APCAL 5000.