HP 35s HP 35s scientific calculator - User Guide - Page 176

What if 70 kg of nitrogen fertilizer were applied to the rice field? Predict the grain yield based on the above statistics. Keys:  Display Description: Enters hypothetical x-value. The predicted yield in tons per hectare. Limitations on Precision of Data Since the calculator uses finite precision, it follows that there are limitations to calculations due to rounding. Here are two examples: Normalizing Close, Large Numbers The calculator might be unable to correctly calculate the standard deviation and linear regression for a variable whose data values differ by a relatively small amount. To avoid this, normalize the data by entering each value as the difference from one central value (such as the mean). For normalized x-values, this difference must then be added back to the calculation of x and xˆ , and yˆ and b must also be adjusted. For example, if your x-values were 7776999, 7777000, and 7777001, you should enter the data as -1, 0, and 1; then add 7777000 back to x and xˆ . For b, add back 7777000 × m. To calculate yˆ , be sure to supply an x-value that is less 7777000. Similar inaccuracies can result if your x and y values have greatly different magnitudes. Again, scaling the data can avoid this problem. Effect of Deleted Data Executing   does not delete any rounding errors that might have been generated in the statistics registers by the original data values. This difference is not serious unless the incorrect data have a magnitude that is enormous compared with the correct data; in such a case, it would be wise to clear and reenter all the data. 12-10 Statistical Operations