HP -25 Owner's Handbook Manual page 71

R, Sy Summation of y values.
R, Xy Summation of products of x and y values.
R 3. x? Summation of x? values.
R, 3x Summation of x values.
In addition, the y-value present before the last press of the
key is retained in the Y-register, while the x-value present be-
fore was pressed is retained in the LAST X register.
To see any of the summations at any time, you have only to re-
call the contents of the desired storage register. (In the case of
the key, recalling storage register contents or keying in a
number simply writes over the number of entries (1) that is dis-
played. The stack does not lift.)
Example: Find 2x, 3x2, 3y, and 2xy for the paired values of x
and y listed below.
Press Display
K [rec] Ensures that all storage registers
are cleared to zero initially.
(Assumes no results remain
from previous example.)
register Ry.
s 122.00 Sum of products of x and y values
from register R;.
=4
21.00
Sum of'y values from register R,.
3
Number ofentries (n = 3).
Mean
The mean (arithmetic average) ofdata entered and summed using
the BB key is available by using the[Z] (mean)key. When you