Plotting experimental data on scales chosen so that the theory gives a straight line allows one to find constants in mathematical expressions. For example, if data are to be fitted to y = ax + b in a plot (see Figure A.1) of y vs. x, b is the value of y at x = 0 and a is the slope.

Figure A.1: Data (x _i, y _i) plotted on linear scales may be fitted to the equation y = ax + b, where b is the value of y at x = 0 and a is the slope.

The following examples are adapted from the fifth edition (1989) of J. P. Holman s book Experimental Methods for Engineers. All of the plotting methods produce a straight line on linear scales and thus facilitate least-squares fitting routines to determine a best-fit straight line. In some of the examples the first paired points ( x ₁, y ₁) are used in plotting the ordinate values.