# Ground Rules Page

The basic ground rules for the Breitling Navitimer Slide rule bezels are as follows:

1. There are two RINGS to this slide rule. The Outer Ring is moveable (the one that rotates when you turn the bezel). The Inner Ring is stationary. It is the ring just inside of, and next to the Outer ring, on the actual watch face itself. I will be referring to the outer and inner ring in all my examples. You must know which is which.

2. There are certain Index Marks on the rings. Most of these are on the inner ring. The index marks are where you need to look to find the answer to your mathematical problem. I will describe where they are with each example, but the most used, and most important one is the red "10" mark that is between the 2 o'clock, and 3 o'clock position on the inner ring. There are others that will be described with specific operations.

3. This is probably the most important ground rule of all. You need to be tolerant of decimal places and powers of 10, and be willing to accept a certain "looseness" with their use. Here's what I mean: the "25" on the outer bezel will be used to represent 0.25; 2.5; 25; 250; 2500, etc., in your calculations. So you need to actually think about what your answer should be (let's say you were doing an equation to determine the weight of a car, and the result you get on the sliderule is "35". The car would be more likely to weigh 3500lbs, than 35lbs). So, as I go through my examples, I will type the number printed on the ring, and after it in parentheses I will type the number it represents. For example, if you need to multiply a number by 460. I will type 46 (460). "46" will be printed on the ring, but you are using it to mean 460 (so say in your head "46 that we are using to mean 460").

4. You will be LUCKY to get one decimal place accuracy. Some times you may have to be satisfied that the answer you get will be "157, and a little bit". If you want 4 decimal accuracy, buy a calculator.

 The Breitling Navitimer World with bezel in the "Home" position