Panasonic HG-S sensor head can be changed safely without turning off the controller. This reduces the man-hours required for the change of line setup for processing of different workpieces, thus achieving a significant reduction of setup change time. Even if unexpected upward thrust occurs, the lower part of the spindle blocks the impact. Damage to the internal structure, including the glass scale, is minimized. The sensor head can be replaced without turning OFF the instrument power. A bending-resistant cable provides peace of mind even when the sensor is installed on a movable tool. Displacement is measured by reading a glass scale with a different slit pattern at each reading position using a high-resolution sensor. This eliminates "value skipping" even when measuring at high speed, and there is no concern of "unset zero point". The controller features the industry's first dual display and offers versatile functions and excellent ease of use. It allows simple and reliable operation of the advanced measurement function in a diversity of applications.