Gompertz Curve Trend Analysis - HP 12c Platinum Reference Manual

Program Instructions:
1. Key in the program.
2. Press fCLEARH.
3. Key in 12 and press ?0.
4. Key in the values for the first 13 months, storing them one at a time in registers 1
through .3; i.e.
Key in the 1st month and press ?1.
Key in the 2nd month and press ?2, etc.,
Key in the 10th month and press ?.0, etc.,
Key in the 13th month and press ?.3.
5. Press g(000t to calculate the centered moving average for the 7th month.
6. Press t to calculate the seasonal variation for that month.
7. Key in the value for the next month (14th) and press t to calculate the moving
average for the next month (8th).
8. Repeat steps 6 and 7 for the balance of the data.
These programs may be customized by the user for different types of centered moving
averages. Inspection of the programs will show how they can be modified.

Gompertz Curve Trend Analysis

A useful curve for evaluating sales trends, etc., is the Gompertz curve. This is a "growth"
curve having a general "S" shape and may be used to describe series of data where the
early rate of growth is small, then accelerates for a period of time and then slows again as
the time grows long. The sales curve for many products follow this trend during the
introductory, growth and maturity phases.
The data points to be fit to a Gompertz curve should be equally spaced along the x (or
time) axis and all the data points must be positive. The points are divided serially into 3
groups for data entry.
The following HP 12C Platinum program processes the data, fits it to a Gompertz curve
and calculates estimated values for future data points. The 3 constants which characterize
the curve are available to the user if desired.
12c platinum / 12C
RPN KEYSTROKES
fs
fCLEARÎ
g°
?+3
d
DISPLAY
000,
23 g°
001, 43
3 ?+3
002,44 40
33 d
003,
12c platinum
ALG KEYSTROKES
fs
fCLEARÎ
Forecasting 83
DISPLAY
000,
001, 43 23
002,44 40 3
003, 33