Coin Identification in Ticketing
Once he observed the platform ticket machines accepted even counterfeit coins. He designed a unique "wise platform ticket machine" which would reject counterfeit coins and needed no external power. It was patented in 1939. The machine was demonstrated before the railway authorities at Bombay in 1941. It satisfied them fully and they placed an order for six more machines to replace the British made machines.
Link: reject counterfeit coins and needed no external power
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