Scale bar
The bar in the bottom-right corner of the map on the website shows what distance a length on screen represents, always in nautical miles. It is a rule of thumb. For an exact distance, use the ruler tool.
Live — updates as you move the map
More detail
How to read it. The bar is a white strip with a figure beside it, such as 10 nm. The strip's length on screen is that many nautical miles on the water. Zoom in and the figure drops. Zoom out and it climbs.
The bar stays in nautical miles even when your Distance setting in Preferences is miles or kilometers.
Why it is not exact. It is worked out east to west at the middle of your view, so do not use it for a north-south distance.
When it is missing. The bar is hidden when the browser window is very narrow. Widen the window and it comes back. It keeps working when the ocean layers have a problem.
The numbers
| How often it updates | Once the map stops moving, not during a zoom or pan |
| How detailed it is | Round steps only: 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500 and 1000 nautical miles |
| Where it covers | The website only |
| Observed or modeled | Neither. Worked out from your map view alone |
| What you see on screen | A white bar with a figure followed by "nm". Always nautical miles, whatever your unit setting says |
Source: the app itself.