The right choice of calibration equipment is, of course, one of the keys to minimize uncertainties. But it is not the only one.
This illustration shows that there are many different components when calculating a single combined uncertainty value. To optimize your calibration uncertainties you have to evaluate and optimize every component in this circle.
Equipment: The specifications on your calibrator.
Object: Does the sensor-under-test have any impact on the reference value of your calibrator?
Person: Is the operator skilled and able to perform the calibration correctly?
Environment: How much do ambient temperature, humidity, mains power variance, etc. impact the reference value of your calibrator?
Method: What method is used to perform the practical calibration task?
With this in mind it is still obvious
to invest in high precision, reliable calibration equipment.