In addition to having your balances calibrated at the appropriate intervals (externally or internally), to really get the most value out of your calibration weight measurements in your daily checks it is good practice to apply the following steps to maximize the precision and accuracy of your measurement results.
Before taking the calibration weight measurements, it is alway good to “warm up” the balance, especially if the balances are analytical or micro balances. Warming up the balance consists of placing the heaviest available calibration weight, either at balance capacity or the calibration weight used to test the high end of the designated user range, and place the calibration weight on and off the balance five to six times in a repetitive manner. This action will help excercise the balance pan and also heat up the coils of the balance. It will help greatly in both the accuracy and precision (repeatability) of your calibration weight measurements.
You then want to do a quick check of the level bubble on the balance and make sure it is centered or fairly center in the circle before taking the calibration weight measurement. This is incredibly important in providing the most accurate calibration weight measurements. If the bubble is not centered, every other precautions taken in your daily checks are out the window.
In regards to enviroment at the time of peforming your daily checks with the calibration weights, you want to make sure that there is no vibration, air currents, temperature swings, opening and closing of doors, or people traffic in your lab near the balance. These environmental issues are sometimes out of our control, but whenever possible should be addressed at the time of setting up your calibration weight daily check program. Very accurate and precise balances (micro, analytical, top-loading, and even high precision scales) are all extremely sensitive to “not ideal measurement” environments. So whenever possible try to be aware of when you are taking your calibration weight measurements. You can’t always control the enviroment or all that is going on around you, but you can somewhat control when exactly you are taking your calibration weight measurements.
Finally, in the placing of the calibration weight on the pan itself, there are a few things we want to remember. Make sure you have a good and steady zero captured. You don’t want the balance to be “noisy” (having the display values running up down five to eight counts very rapidly) at the time of placement of the calibration weight. You also want to take a degree of care and technique in your placement. Try not to be too heavy or too rough in placing the calibration weight on the pan. Lastly, place the calibration weight in the most center of the balance pan. Having the calibration weight, or any measurement sample for that matter, properly centered will help minimize the effects of any corner-load error.
It seems like a lot, but if we do keep the above in mind and apply these when taking our calibration weight measurements and also our sample measurements we will surely be getting the most accurate measurement values available.