Section 6: Functions continue101
Keystrokes Display
9 ENTER
 9

8 Σ+
 3
Third pair is accumulated; n = 3.
RCL 11
 16
Sum of x values in R11.
RCL 12
 98
Sum of squares of x values in R12.
RCL 11
 21
Sum of y values in R13.
RCL 14
 155
Sum of squares of y values in R14.
RCL 15
 122
Sum of products of x and y values in R15.
RCL 16
 3
Number of entries (n = 3).
g CLX
 – 0

Note: If your data {xi} or {yi} contains many redundant leading digits, you should refrain from copying them into the calculator. For example, if your x-data is {999999999, 1000000001, 1000000002}, you should enter the x-data as {–1, 1, 2} and add redundant digits to any x-related answer produced.
Mean
The MEAN function is used to calculate the mean (arithmetic average) of x and y values accumulated in the statistical registers. When you execute MEAN :
 1. The mean of x is calculated using the data accumulated in the first and last statistical registers. (These are the registers that contain Σx and n; presently defined as R11 and R16.) The resultant value for mean of x is placed in the X-register. 2. The mean of y is calculated using the data accumulated in the third and last statistical registers. (These are the registers that contain Σy and n; presently defined as R13 and R16.) The resultant value for mean of y is placed in the Y-register. Simply press X Y to bring that value into the X-register for use.
The easiest way to accumulate the data required for the MEAN function is by using the Σ+ function as described above.
Standard Deviation
The SDEV function is used to calculate the sample standard deviation (a measure of dispersion around the mean) of data accumulated in the statistical registers. When you execute SDEV :
 1. The sample standard deviation of x is calculated using data accumulated in the statistical registers containing Σx, Σx2, and n. (These registers are presently defined as R11, R12, and R16.) The result is placed in the X-register. 2. The sample standard deviation of y is calculated using data accumulated in the statistical registers containing Σy, Σy2, and n. (These registers are presently defined as R13, R14, and R16.) The resultant y value is placed in the Y-register. Simply press X Y to place the y value in the X-register for use.