SOP For calibration of weighing balance is described in this post which you can follow in the section of the Quality Assurance Department.

This procedure is established to provide a system for the calibration of weighing balance.
This procedure is applicable to all the weighing balance being used in Plant.
Q.A Officer
Manager Quality Assurance
Note down the relevant Information of Instrument In the In House Calibration Data Sheet.
Measure the ambient temperature and relative humidity with the help of calibrated Hygrometer and note the reading in the column marked as environment condition in the In house Calibration Data Sheet.
Before calibration, clean the instrument.
Adjust zero error if applicable Check levels of balance also and adjusts if required.
Take calibrated weights and note down the reading in column marked Set Value In the In house calibration data sheet
Place the weight on scale and note down the reading of scale in the column marked Observed Value
Repeat step 5.5 and 5.6 for other respective readings.
Calculate the deviation by subtracting the set value from the observed value take average, and enter the average deviation in the column marked "Average Deviation" in the In House Calibration Data Sheet.
Enter master Instrument Average Deviation in the column marked "Master Instrument Avg. In the In House Calibration Data Sheet
Add Avg. Deviation and Master Instrument Avg. Deviation in the column marked Net Deviation.
Now analyze the net deviation If It Is out of the specified deviation (least count), the balance Is to be adjusted until the deviation come within required deviation If after adjustment deviation does not come within the range of specified deviation and required accuracy, stop calibration and issue a ‘RED" slicker marked as REJECTED" to instrument and fill the In House Calibration Data Sheet accordingly. If the net deviation is within specified limits then affix the calibration sticker on the balance. Calibration Coordinator prepare the In house calibration Data Sheet and submits to concerned calibration in charge.