Last week I posted a story showing the World War II Royal Air Force navigator’s map reading light that I have and that I used in one map reading rally. After trying and fabricating several map reading potis I settled on a simple poti that I modified so that I can fit it anywhere with any scale in a matter of about five minutes. This is useful because one local rally uses a map with a scale that is not commonly used. My poti is shown below.
My poti came with an open bottom that rests on the map. The reading lens has a diameter of about 90mm and provides two-times magnification of the map. The handle on the left side of the poti is useful to me because it frees my right hand to make notes. Because it has an open bottom I was able to piece together a homemade scale bar that I can add to the poti in order to estimate distance on the map. I can change the scale to suit any scale used by the rallymaster or that matches the maps being used. Below I show the scale bar that I made for the 1:150,000 scale maps that I have collected for the Monte Carlo Rallye Historique. Each major line represents a 1.0 kilometre with the shorter lines representing a 0.5 kilometre. Note that there is a set of lights that ring the inside of the poti which can be turned on to greatly aid reading the map in night rallies and be useful during day time map reading as well. The unit draws its power from a cigarette lighter power plug.
My Homemade Scale Device
I can add a second scale on the opposite edge of the bar if two map scales are required, therefore I have complete flexibility.
Another feature of this poti is an access hole on the right side of the poti. This is shown below.
Map Access On Side Of Poti
With this access hole I can insert a pencil into poti which allows me to add marks, notes, or distances to the map without removing the poti from the map. Having a small scale bar maximizes the open area where I can add information to the map.
Pencil Can Be Inserted To Mark The Map If Needed
The image below shows how distances can be estimated using this device. These images were taken in the darkness, only using the light from the poti.
Example Of Estimating Distance On A Map
Some roads, such those in the area of the legendary Col de Turini shown below, are so crooked that distances are hard to measure, but intelligent guesses can be made as you get used to the map length of a kilometre.
Some Roads Are Too Crooked To Easily Use The Measuring Scale
I am very pleased with my poti. It has all of the features and flexibility that I need to meet the challenge of any rally.