What can I use to Measure Visibility?
The best thing is a really good pair of binoculars or a telescope. These can be bought from a number of different shops and equipment suppliers. In your local high street you should be able to get a reasonably good pair of binoculars quite cheaply.

The other thing you will need is a good map of the area. Most maps will do, but if you borrow or buy one, it needs to have a fairly large scale on it so that you can see about 100 km around the location of your weather map.

Using your Map
The easiest way to measure distances is to look at the scale and identify distances of 1km, 10km, 20km, 30km, 40km, 50km. Measure a piece of string for each distance. Then pin one end of the string where your weather station is situated. You can then use the other to find points of reference on your map within the circumference of that distance. Look for churches, buildings, hills, pylons or other tall features. If you know where a particularly recognisable tree is situated you can use this too. You can then take the map out with you when you make your observations.