By turn indicator I presume you're referring to the standard 'Bat & ball' Turn & Slip' instrument (TI). This instrument most certainly contains a gyroscope!
The difference between the TI & the Turn Coordinator (TC) is that the TC has the axis of rotation of its gyro inclined by ~30deg. This makes the instrument sensitive to forces in two planes of motion: yaw & roll.
A spin involves moving all planes so the TC will respond to rolling forces, not just yawing/turning.
Last edited by Tinstaafl; 11th Jun 2002 at 22:05.