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I notice that people seem to scan their tickets twice, on entry and exit, on the NS system (Intercity / Sprinter) in Amsterdam. Since the officials scan your ticket on the train, what's the purpose of scanning on the platform? I've tried with my one-way tickets and usually the scanner beeps and flashes, though once it flashed green.

I notice that people seem to scan their tickets twice, on entry and exit, on the NS system (Intercity / Sprinter) in Amsterdam. Since the officials scan your ticket on the train, what's the purpose of scanning on the platform? I've tried with my one-way tickets and usually the scanner beeps and flashes red, though once it flashed green.