Final answer:
Factors affecting auto calibration include temperature variations and electromagnetic interference. A more sensitive digital device could improve the accuracy of null measurements by detecting smaller potential differences. AC current is more likely to interfere with compass readings due to its changing magnetic field.
Step-by-step explanation:
Two factors that could affect auto calibration are temperature variations and the presence of electromagnetic interference.
Regarding the accuracy of null measurements, other factors limiting accuracy can include instrument precision, operator skill, and ambient conditions. A digital device that is more sensitive than a galvanometer could potentially improve the accuracy of null measurements. This is because more sensitive instruments are capable of detecting smaller differences in electrical potential, leading to finer adjustment and, consequently, more precise null measurements. However, it is also essential to ensure that the digital device used for such measurements is calibrated and free of its own sources of error to truly enhance accuracy.
As for compass readings, AC current in your refrigerator is more likely to interfere with them than the DC current when you start your car. AC current generates a changing magnetic field which can cause compass needles to fluctuate and provide unreliable readings, while DC typically produces a steady magnetic field.