HP HP-18C User Manual

BEl
2,615,00
Displays the CALC menu .
IBDI
~lEA~1=435, 83
Calculates the mean.
..
MEDIAN=395,00
Calculates the median .
IiiID
STDEV=231,55
Calculates the standard
deviation.
..
Displays the rest of the
CALC menu.
..
~lIN=175,00
Displays the smallest
number.
Curve Fitting and Forecasting
Curve fitting is a technique for finding a mathematical relationship
between two sets of numbers. The two sets of numbers are referred to
as x-values
and y-values. Curve fitting uses two SUM number lists-
one for the x-values and one for the y-values. You can select one of
four relationships (or models*), which are illustrated in figure 6-5:
• Linear;
y = A + ax (A is the y-intercept, a is the slope of the line).
• Logarithmic;
y A + a In x (all x-values must be positive).
• Exponential;
y
Ae Bx (all y-values must be positive).
•
Power curve; y = AxB (all x-values and all y-values must be
positive).
The HP-18C uses the x- and y-values to calculate A, a, and the cor-
relation coefficient.
The correlation coefficient measures how well the
calculated curve describes your data. Once the curve has been calcu-
lated, it
can be used to do forecasting (what if?) calculations.
• The HP-18C calculates the exponential, logarithmic, and power models using transforma-
tions that allow the data to be fitted by standard linear regression. These transformations
are:
• Logarithmic; y ~ A + B In x; y versus In(x).
• Exponential; In(y) ~ In(A) + Bx; In(y) versus x.
• Power curve; In(y) ~ In(A) + B In(x) ; In(y) versus In(x).
102 6: Running Total and Statistics Calculations

HP HP-18C Specifications

General

Brand	HP
Model	HP-18C
Category	PDA
Language	English