### 2. Principle

#### a. What's a "pace"?

Hard to believe, but we can take the simple action of walking and over-complicate it to measure distances.

The chapter title is Pacing, which is pretty generic. But what constitutes a pace? And does it differ from step or stride?  Does it make a difference if we count it every time the left foot lands, or the right foot, or either foot?

To keep it simple, we will define pace as the unit measured each time either foot lands. That's pretty easy to remember and apply.

But wait, we still have an issue: our feet themselves have length, Where on our feet does a pace begin and end? Figure B-2 shows four different ways we can define a pace.

 (a) Heel-to-Toe (b) Toe-to-Toe (c) Heel-to-Heel (d) Arch-to-Arch Figure B-2Pace

Heel-to-Toe, Figure B-2(a), shouldn't be used because it has an undefined space between successive paces; the others are fine. Which to use is a matter of personal preference although Heel-to-Heel, Figure B-2(c), allows pacing to start at the base of a wall, Figure B-3.

 Figure B-3Starting at a Wall

#### b. Calibration

Most linear units (with a few notable exceptions) have fixed length regardless where applied, but not everyone's pace is the same length. Expressing a distance in paces (or area in square paces) is ambiguous and must be converted to some conventional unit others can understand. This requires a conversion factor, determined through a calibration process.

For reliable results, calibration should be performed under controlled conditions.

##### (1) Calibration conditions

Open flat base line path allowing uninterrupted pacing in both directions

Lay out a base line that is 100 to 300 feet long.

Establish base line length to a higher accuracy than pacing

Warm windless day

Shoes and clothes typically worn in surveying field situations

##### (2) Procedure

Base line should be paced at least three times and until at least a 1/50 precision is consistently achieved

Reasonable resolution is a half pace.

All pace counts are recorded, those outside the precision will be rejected for subsequent computations

Compute conversion factor and pace count.

Conversion factor is base line length over the average pace, Equation B-1.

Pace count is the number of paces per 100 feet (or 100 meters), Equation B-2.

 Equation B-1 Equation B-2
##### (3) Application

For highest accuracy, pace the unknown distance enough times to achieve consistently.

Apply either the conversion factor or pace count to determine the unknown distance.

How accurately can a distance be determined by pacing? As we'll see in the Errors section, there are a number of things which can affect pacing. Remember that pacing resolution is about a half pace which for most people is between 1 and 1.5 feet. Obviously that resolution does not support distance determination to a hundredth of a foot. It's best to use the rules of significant figures to express a paced distance to a reasonable level of accuracy.