How to read a pressure gauge
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I would like to ask: when reading a pressure gauge normally, we read it according to its scale. As shown in the pressure gauge in the figure below, if the pointer is at 0.05, does that mean the pressure is 0.05 MPa? Some people say there is a circle on the dial with ‘2.5’ inside it; if the pressure is 0.05×2.5, which one is correct?
If calculations are still needed, then the dial markings are meaningless. Conversely, why not go straight to it?
If the pointer is at 0.05, the pressure is 0.05 MPa. There is a circle on the dial with “2.5” inside it, indicating that it is a pressure gauge with a precision level of 2.5. This pressure gauge has a range of 0 to 0.25 MPa and an accuracy class of 2.5; the allowable error between the pressure value indicated by its pointer and the actual pressure of the medium being measured shall not exceed 0.25 MPa × 2.5% = ±0.00625 MPa ； When the pressure gauge indicates a pressure of 0.05 MPa, the actual air pressure is between 0.04375 and 0.05625 MPa.
What is indicated inside the circle represents the accuracy class of the pressure gauge; the reading is taken directly from the scale.
The reading indicated by the pointer is the pressure value, and the 2.5 inside the circle represents the accuracy grade
A pointer reading of 0.05 corresponds to 0.05 Mpa (if the scale is in Kpa, then it’s Kpa); 2.5 represents the accuracy grade, and it has nothing to do with the actual reading.