Philip Harris Ticker Timer

"This extremely popular unit has revolutionised experiments because of the quality of the traces it makes, and the reliability of the mechanism ensures that ticker-tape experiments are no longer hit and miss.
There is no double-dotting or smearing, even at high speeds. No pen or carbon discs are required. Friction between tape and ticker-timer is kept to a minimum. Excellent results can be expected. The unit comes with a boss-head so that it can be easily clamped in a rod. Requires 2-4V AC from a low-voltage power supply. The unit is protected by a 2A internal fuse. Uses self-marking paper tape. Self marking tape is not included."