Within the sport of TSD Rally there can be several different classifications for competitors and allowable equipment. In local clubs there may be a Novice class for newcomers who will obviously not be competitive by lack of experience. A Novice entry may be awarded a trophy just for entering the event if they are the only Novice entry there. Rules for graduating from Novice class can vary, like after running four events, or the first or second time that you beat another Novice class team.

The next class up might be SOP, or "Seat Of the Pants" class. This means you drive and compete with little or no instrumentation other than the standard car speedometer and odometer, and any kind of clock or watch you might have in your possession. Other equipment may be limited to pencil and paper, or possibly a four-function calculator (depending on local club rules).

A top class for local club events might be Navigational class. In this class you can use any kind of equipment you like, including electronically adjustable odometer connected to an electronic computer.

For larger and better organized TSD Rallies there can be other more strictly defined classes. For instance, Stock class may allow any car with standard odometer and speedometer, any clock or watch, a four-function calculator with one memory, but no other electronic equipment. This is getting a little tougher to enforce these days with so many cell phones and GPS units, possibly built into newer cars.

For us vintage car folks there may be a Vintage class. This used to be limited to cars more than 25 years old, but may now be limited to cars built before 1981. Equipment allowance is also quite sparse. You may use only the car's original speedometer and odometer, only mechanical clocks and stop watches (no digital wrist watch allowed), and any kind of purely mechanical calculator (including a slide rule if you know how to use one). This has its own unique class of vintage mechanical instruments which will be the subject of a following article.

The top class here may be called Unlimited class, which is rather like Navigational class in allowing any kind of computerized instrumentation you like. Taking one small step back has a class called Limited class. This is similar to Unlimited class, but does not allow any direct connection between the odometer and a computer. I suppose this was intended to accommodate folks with mechanically or electronically correctable odometers and a laptop computer.

Now into the 21st century we have cars with built in navigational systems and GPS. These devices don't necessarily do much for TSD rally when you don't know where you're going and don't care where you are (except to follow the designated route). The GPS may give some idea of average speed between pushes of a button, and they might show you a road map ahead before the roads may be in sight. Shy of placing these cars into Navigational or Unlimited class, I don't know if formal rally groups may have defined some new class for these cars. Perhaps it depends on how many of them show up for a given rally. If everyone was driving modern cars, they might all be in Navigational class.