Examples of all calculations used in data reduction must be presented. This implies the proper typesetting of equations as discussed in Chapter 9. Choose one set of raw results and carry out all calculations that lead to the calculated data that will be discussed later. Choose data that are representative of the whole lot. The first data taken are usually a bad choice since you are still unfamiliar with the measuring devices. It is important to start out with raw results to ensure that all calculations can be reproduced. If stress was measured using a transducer whose output is in volts, include a sample of a calculation reflecting the conversion of volts to megapascals.
All calculations using theory presented in a previous section of your report should be refered to as such. For example, a preamble to a sample calculation could be: strain was calculated using Equation X.X. Do not reiterate what is implied by Equation X.X. It can be found in your theory section.
The Calculation section can be tedious to read, especially to one who is verifying the correctness of the calculations. Make it thorough but concise. Use an appendix if large sets of calculated data are involved. Show sample calculations that lead to intermediate values but do not tabulate these values. Tabulate any values that will be used in later sections of your report.
When preparing results containing measured and/or calculated values, remember to make sure that the number of significant digits is meaningful and reasonable. To do this you must carry out uncertainty calculations. For example, if reporting a calculated yield stress, more than three significant digits are likely to be unreasonable. It is common to find yield stresses such as 345.124MPa listed in lab report results. This is an unreasonable number. The load cell of a typical testing machine has a relative uncertainty of ±0.1%, which represents approximately ±0.4MPa for the stress in this example. On the basis of this condition alone, the yield stress of the sample could actually be as low as 344.7MPa or as high as 345.5MPa. Furthermore, taking into account the inherent variability between samples (easily ±1%), one soon realizes that the yield strength of the material can only be represented reasonably by a number like 345MPa based on realistic and careful measurements. Do not forget to present the units for all the results in a table.
Units and units conversions are a necessary evil of engineering
calculations. Show units conversions in sample calculations. It is bad
practice to hide conversion factors in proportionality constants.
Heywood [5] gives a perfect example of this misleading
technique stating that in U.S. units (whatever those are) engine power
can be calculated from engine speed 
and torque 
using
Equation 4.1. The value in the denominator is not a
constant but a conversion factor that not only masks the conversion of
shown units but also the conversion of revolutions to radians.
