A micrometer, including a constant force drive spring actuator configuration, is disclosed which comprises a frame, an anvil, a spindle, a linear displacement sensor that senses a displacement of the spindle, and an actuator including a button which is configured to move the spindle toward or away from the anvil. The spindle drive is attached to a constant force spring actuator comprising at least one constant force spring coil extending toward the spindle and attached between the spindle and the frame such that the sum of their forces drives the spindle toward the anvil with an approximately constant force. In some embodiments, the constant force spring actuator comprises at least two parallel constant force spring coils, extending in parallel toward the spindle. The constant force spring may be made more compact, exert a greater force, and have an extended life relative to known configurations.