Rulex OS map scale card scales: 1:25000, 1:50000 and 1:40000 and Naismith's Rule

Rulex

The Rulex Map Scale Card is a credit card size scale ruler specially designed for Ordnance Survey maps.\nThe handy credit card size makes scale cards easy to carry in your pack, pocket or wallet.\nThey feature the most popular OS map scales \u2013 1:25000, 1:50000 and 1:40,000.  \nSo you can measure distances accurately to within 25m (at a scale of 1:25000).\nThe card also features a depiction of Naismith\u2019s Rule which helps you to calculate the time that your walk will take.\nScale cards are made from 1mm thick flexible ABS plastic and are UK manufactured.\nOne map card supplied in a sealed polybag.