Two photo gate can be fixed any where on the post which is 1600mm in length with a rule.
The basic free fall experiment Free Fall Adapter enables accurate and repeatable measurements of the acceleration of gravitational acceleration ‘G’ on Earth. 
Supplied four steel balls (two 19 mm and two 16 mm diameter).
This product includes a  magnet ball releaser on the top being controled by the Timer (not included). 

Science Lab Supplies is a leading G Free Apparatus manufacturers, suppliers and exporters that offers wide range of G Free Apparatus at most competitive prices.

G Free Apparatus

SKU: SL-449