Most graphing calculators have a function called linear regression which can be used to find a precise line of fit, using strict rules. This line of fit is then called the line of best fit or the regression line.
The first step is to enter the data points in the calculator. On a TI calculator, this is done by pressing the button, and then selecting the option
This gives a number of columns, marked L, L, L and so on.
With the help of the arrow keys, choose where in the lists to fill in the data values. Enter the data points' values in list L and the corresponding values in list L Values are entered into the fields using the number buttons followed by
Fitting the Line
After entering the values, press the button, then select the menu item CALC to the right.
LinReg() gives a line of best fit, expressed as a linear function in slope-intercept form.
DiagnosticOnand enable it by pressing twice. Then, find the line of best fit again.