What intervening variables that could affect the performance of a freely suspended compass and linear measurement?

Many intervening variables that could affect the performance of a freely suspended compass and achieve a linear measurement. Some of these variables are enumerated below but not limited to these items.
1. Temperature Induced
2. Current Stabilization
3. Temperature effects on the materials
4. AC and DC

"pacesetter of the south," comma inside the quotes

Answer your driving test ;