The focus in an electrophysiological analysis is the physical health of the cell. This is represented by a reliable, steady, and deep (hyperpolarized) resting membrane potential. A high membrane resistance is also necessary for an electrophysiological analysis. For any condition, many cell membrane potentials should be measured (at least three to ten cells) to establish the baseline, control level. Normal ciliary beating should also be observed. When a cell is damaged, it is often easy to see irregular or slowed ciliary beating, indicating either an uncoordinated or depolarized state. If a resting membrane potential has been established, an irreversible depolarizing drift may also indicate cell damage. A decreased membrane resistance is also an indication of cell damage. A good test of cell condition is to induce an action potential by current injection through the membrane potential recording electrode. This is easily done by using a 1-nA electrode resistance calibration pulse that is commonly a feature of modern recording devices. If the cell shows a visible jerk backward, it ensures that the electrode is inside the cell and that the cell is healthy enough to show a strong response.