An old rule for a new rallyist

This is probably one of those posts that will be of interest to those friends of mine who don't road rally and are curious as to what makes it such a fascination for me (and my wife). For you more experienced rallyists the article might illicit a wry smile or two.

The road rally world of today is driven by expensive computers. Big black boxes that sit on the dashboard and tell you how fast/slow you're going in relation to your actual time, how far you've gone/got to go, even counting your time to the perfect arrival time. Even now though these big black boxes are being replaced by iPad apps that do exactly the same for 5% of the price. So it's fun to think back the old days and see what rallyists used then.

This is one of those pieces of equipment. A Stevens Rally Indicator or Stevens Wheel. 

It's basically a circular slide rule. They came in two sizes 6" diameter and 10". This is the six inch version. The ten inch was more popular because of the larger size meant larger, easier to read numbers, especially at night. 

What I'm doing with a slide rule I don't know after my brushes with them in school. I can well remember having a small circular slide rule, when everyone else had a straight rule. 

"So Holmes." Said Rob Morton, maths teacher at Queen Elizabeths Grammar School Alford. " A circular slide rule. Whats three multiplied by two?"

I diligently set to rotating the wheels and sliders to do the calculation.

"Six" I said proudly, having  worked quite hard to get the calculation right. 

"Well done." The teacher said. To this day I'm not entirely sure if he was taking the Mickey or not. I think I heard a few giggles go around the classroom. 

So, how does this disc of plastic work for the rallyist?

As you see, there are three arms. The large one is marked T the two smaller ones E and M. 

When you go out on a rally the first thing you do is check how accurate your cars odometer is compared to the rally official distance on a special "Odo Check" section. This is what the E and M arms are for. At the end of this stage you set the M arm to read the official miles and the E arm to what your cars odometer reads. This takes care any measuring errors. Now set the T arm to the speed for the section of the rally you're ready. In this picture it's set at 43mph. A somewhat brisk pace.

Right, let's say you need to know how long it's going to take you to drive 11miles at the 43mph pace. You move the E arm to 11 and then read off the T arm. It says 19.8 minutes. Point eight minutes? You sound confused. Don't forget you also have the Galco hundredths reading stopwatch from a few posts ago. That's what you'll be using to time the leg.

Easy.

Now let's say you need to know how far you've gone in a certain time. You set the T arm to the amount of time that has passed. Let's say 11 minutes. Then if you look at the reading on the smaller E arm you see it says 6.45. You've travelled 6.45 miles! Calculations like this are the bread and butter of road rally, and I know of contestants who, in this world of the high tech black boxes I referred to at the start of this piece, still use the Stevens Wheel today to great effect. Road Rally is a sport that doesn't have to be run using the highest of tech.

To me it's just a bit of a novelty thing to have at the moment. It would though, be rather fun to compete in a road rally using one. 

After my first brushes with the slide rule at school all those years ago, I never thought I'd buy another one let alone consider using one.