[Matra et Alpine]

Maps used in navigational rallies in the UK are based on the Ordnance Survey OS LandRanger 1:50,000 scale maps.
On a map there is a series of intersecting grid lines; one set runs vertically up and down the map, the other horizontally across the map. The grid lines are 2cms apart, representing 1 km in real terms. All are consecutively numbered so that each square can be identified by a four figure number, two identifying the horizontal grid line and two the vertical grid line.

Therefore, viewing the attached map, the town of Elphinston is in square 3970 on Map 66. Note the horizontal number comes first ( easiest remembered by "you go in the door and up the stairs" ). The numbers are printed in light blue on the OS maps beside the gridlines. ( Some navs will highlight or repeat these numbers to speed up plotting in the car )

Specific points on a map can be identified by the use of six, eight or ten figure references.

6-figures == HHhVVv
In a six figure reference, the first two numbers (HH) denote the horizontal grid line, the fourth and fifth numbers (VV) the vertical grid line. To plot a reference simply find the horizontal grid line and follow it up until it intersects with the vertical grid line. The position you now have is the bottom left hand corner of the square containing the reference.

To locate the exact spot use the third and sixth numbers of the reference, this is where a romer comes in. The third figure (h) is the number of tenths across the square and the sixth (v) the tenths up the square. The greater the number the further across or up the plot will be; for example xx0xx0 will be the bottom left hand corner of a square, while xx9xx9 will be almost the top right hand corner.

At times complete numbers are not accurate enough to identify the road, junction or landmark, so then fractions are added to the third and sixth figures.

8-figure reference == HHhhVVvv
Now an extra digit is added to each gridline to give a more accurate refrence.
Now each gridline is broekn into 100ths.
This will commonly only be used for 1/2 of grid tenths.
These are usually accurate as it needs to be on the Landranger series.

10-figure reference == HHhhhVVvvv
This leads to the more common item, the ten figure reference; in this the fraction is replaced by a two figure decimal fraction. This means you end up with a reference such as 1235045625, which is equivalent to the six figure reference 123½456¼. These would typically only be used on higher detailed maps and unlikely in normal use.

So if there are only 4 digits, it is a box. 6 digits is 'standard' and the scale for romers for 1:50000. 8 digits will be used occasionally where it is necessary to go more detailed and 10 digit for further details. Commercially available romers won't go below 6 digits. So nav skill usually becomes necessary to interpolate.

Most events that you'll contest, certainly most road rallies, will use a fairly straight forward system. There will be a list of controls, defined by references, with, maybe, the direction of approach and/or depart being stipulated for some controls. The navigator plots these and then selects the quickest route between them.

On the vast majority of events pre-plot navigation has become the norm these days. With pre-plot events the route information is given out with time being allowed for a navigator to plot the route prior to starting the competitive sections. In these you will be given the route information, then go to a holding control for an hour or so, before the first competitive section.

On some events plot'n'bash navigation is used. As the name suggests, the navigator isn't given the route card until the due depart time. This gives the crew a choice of either plotting on the move or stopping and plotting the route before continuing. Obviously the first option means less time lost, however it's a very difficult task to simultaneously plot the route, keep the driver on the correct road, deal with controls and also ensure that the contents of your stomach don't come loose!

For beginners the best choice will be to stop and ensure the correct route is on the map before embarking on the section

Within this little challenge you'll get to experience all the 'fun' of navigational challenges with out the gut-wrenching yuumps and sideways cornering any driver would no doubt throw your way. So when you are feeling confident in doing these tests, just get the rest of the family to move the desk and your chair while you try it and you'll start to experience the real world of club navigating

BTW, a little piece of 'net logistics here. If you print the maps and romer there is a certainty they won't be the same scale. Not much I can do to help other than suggesting you use a graphics package to ensure they are all printed at equal 1:1 scale. I can't help you with that, you'll need to sort it out on your own computer/printer. Oh and ask the ink-buyer for permission first.

The map is (C) Copyright Ordnance Survey.
The romer is (C) Copyrigh Don Barrow. see www.donbarrow.co.uk