Explanation of vending, top-up and collection machines
The Man in Seat 61 on Twitter: "Just put these RET metro ticket machines through their paces. A one-shot ticket costs €4, not as bad as I'd feared for a 'smart carded'
Check OV chip card balance and top up automatically - Techzle
OV-chipkaart – Travel guide at Wikivoyage
How to top up a Netherlands Ov-chipkaart 5 January 2018 - YouTube
OV-Chip Card - Public Transport in Amsterdam and Netherlands
Chipcard designs, themes, templates and downloadable graphic elements on Dribbble
OV-chipkaart - Wikipedia
Jumbo Oostburg - Eindelijk is ons OV-chipkaart oplaadpunt... | Facebook
Topping up the balance on your OV-chipkaart | NS
Travelling with the OV-chipkaart | Travel information | NS