Take a measurement with nothing in the gauge. That reading is the zero-error.
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Suppose say you have plastic rule new one. There you will be having zero marking. When you have to measure the length of a rod then you would keep zero marking at one end of the rod and the marking where the other extreme of the rod is taken to be length of the rod. say it is at 4 cm. So 4cm is the length. And suppose the ruler is an old one whose edge got damaged. Now you don't have zero marking so visible there. So you have keep the end of the rod at say 1 cm marking. Now the error that we commit is known as zero error. Here the error is positive. ie +1 cm. So as the other end of the rod is at 5cm marking then the correct length is got by applying zero correction. As zero error is +1 cm, then zero correction would be -1 cm So the correct length 5-1 ie 4 cm. Same way in case of vernier, if zero of vernier is at left side of zero of main scale, then the zero error is negative. If zero of vernier is right side of zero of main scale then error is +ve as we have seen in the earlier old ruler case. Same way in case of screw gauge as the head scale zero is above pitch line then error is negative and as head scale zero is below pitch line then zero error is positive.
step-1:remove the pressure gauge from the equipment when machine is in off condition. step-2:remove the cap and glass of the gauge. step-3: remove the needle of the gauge with a needle puller( a special tool ) step-4: place the same needle indicating zero. step-5: fix the glass and cap as usual. step-5: check(calibrate) the gauge on a dead weight tester with a master degital pressure gauge.
the correction which is made to get correct measurement after zero error
Zero error in an Essae weighing machine refers to the condition where the scale does not read zero when there is no weight on the platform. This error can occur due to mechanical misalignment, calibration issues, or wear and tear of the components. It is important to identify and correct zero error to ensure accurate measurements, typically by adjusting the zero balance or recalibrating the machine before use. Regular maintenance and calibration help minimize zero error and improve weighing accuracy.
The scale doesn't start at zero, so you need to compromise or you get a systematic error.