I have been using a Sigma 800 odometer for measuring cycling distances and an Excel table to keep track of them plus maximum and average speeds. However, there is a device that can do all that and more automatically and it's called Garmin Edge 200. It's a GPS device that records speed, distance, average speed, maximum speed and changes in elevation while also keeping track of your route. When you upload the data to the Garmin Connect site, you can view your route on a map or a satellite photo.
For a one-speed bicycle, my Jopo is certainly accumulating brackets for different devices. I won't be removing the Sigma installation as long as it works, but I probably won't be using the odometer very often from now on. The place there was left to install the Garmin bracket was near the right handle, where it is easy to see and reach even during cycling.
The ones in the middle are the Sigma odometer and a bracket for a led light, which I did not use today as I was out around noon and visibility was good enough.
I took the odometer with me on this test run to compare the readings from it and the GPS device. There were differences, but they weren't really significant. Some can probably be explained by the different measuring methods. The odometer simply counts the rotations of the front wheel, while the GPS records location data. Anyway, the differences were small and as long as you use the same device, the figures can be compared with each other.
When I took the bicycle out from the storage and started the GPS device, it took fairly long for it to find satellites. That's probably because I was standing by an 8-story building and the visibility to north-east, east and south-east was totally blocked by it and two other houses. At the other end of the route, by the supermarket I visited, the device found the satellites immediately at power on, probably because I turned it on in exactly the same place I had turned it off 20 minutes earlier.
As I loaded the data to the Garmin Connect site, I was surprised at how accurately the route was shown on the map, but I like the satellite picture even better. Now I don't need to draw the routes on a paper map anymore.