Section 6: Functions continue103
Keystrokes Display    
  XEQ _ _    
  Average minimum inches or rainfall per month (mean of x) is in the X-register.
X Y 
  Average maximum inches of rainfall per month (mean of y) is in the display.
  XEQ _ _    
  Standard deviation of minimum rainfall per month (x values) is in the X-register.
X Y 
  Standard deviation of maximum rainfall per month (y values) is in the display.
The illustration below shows what happens in the stack when you execute MEAN of SDEV . The contents of the stack registers are changed...
  ...from this... this.
T  t  
      T    t
Z  z  
      Z    z
Y  y  
lost.   Y MEAN of y or SDEV of y
X  x  
      X MEAN of x or SDEV of x
    LAST  X    x
Deleting and Correcting Data
If you key in an incorrect value and have not executed Σ+ , press CLX or    to delete the incorrect number or digits, and key in the correct number.
If one of the values is changed, or if you discover that one of the values is in error after you have executed the Σ+ function, you can correct the summations by using the Σ– (summation minus) function as follows:
  1. Key in the incorrect data pair into the X- and Y-registers.
  2. Press g Σ– to delete the incorrect data.
  3. Key in the correct values for x and y. (If one value of an x, y data pair is incorrect, both values must be deleted and reentered.)
  4. Press Σ+ .
The corrected values for mean and standard deviation are now obtainable by executing the MEAN and SDEV functions.