Chart Scale Reader

What it does

• A chart ratio of 1:50,000 is not a distance until it is converted to a ruler.
• The reader returns centimetres per mile and the smallest resolvable feature.
• Useful when deciding which chart to carry for a short leg.

How to use it

1. A larger denominator means a smaller scale and less detail.
2. Check the print scaling before trusting a measured distance.
3. Small-craft charts often fold scale changes along one sheet.
4. Record the chart edition date beside any measured distance.

Safety notes

• A measured distance is only as good as the chart edition it came from.
• Do not plan a passage on a scale too small to show the hazards.