Page last updated
Tuesday March 10, 2009
Credits:
I didn't create this calculator; I adapted it (with permission) from the
original which
is at
http://web.mst.edu/~gbert/JAVA/uncertainty.HTML
.
Here's an
OGG video
about how to use the calculator.
Uncertainty Calculator
This is a device for performing
calculations involving quantities with known or estimated uncertainties.
This is known as
error propagation or
uncertainty propagation.
It calculates uncertainties two ways:

most probable uncertainty,
also called standard error (or uncorrelated uncertainty),
which is used when
errors
are independent;

maximum uncertainty,
also called maximum error (or correlated uncertainty),
which is
used when they are not.
There are a couple of radio buttons to choose which type of uncertainty
you want to use.
Why is there no equals sign?
This calculator operates in what is known as
postfix mode.
That means you input your values for X and Y first, and
then
you choose what you want to do with them.
This will be explained later in the section under
Operation.
(In many ways this actually makes it easier to use once you get used
to it.)
What calculations can I do?
The calculations may involve algebraic
operations
such as:
 Z = X + Y
 Z = X  Y
 Z = X * Y
 Z = X/Y
 Z = X^{Y}
or mathematical
functions
of
the type:
 Z = 1/X
 Z = X
 Z = ln(X)
 Z = log_{10}(X)
 Z = 10^{X}
 Z = e^{X}
 Z = sqrt(X)
 Z = X^{2}
It also includes trigonometric functions.
The trig functions assume angles are in radians.
There are also functions to convert between degrees and radians.
If uncertainties (dX, dY) are
provided for the input quantities (X,Y), the program will perform the operation
or function to calculate the answer (Z) and will also calculate the uncertainty
in the answer (dZ). The program will assume the value has no uncertainty
if an uncertainty is not provided.
FZ and FdZ refer to formatted versions of Z and dZ. These are still being
developed (ie. they may not be quite right at present.)
Operation:
Position the
cursor on the blank under "X", click the mouse, and type a value.
Alternately, press the TAB key until the cursor appears in this blank,
then type the number. In case of an error, use normal textediting
procedures.Enter values for X and dX, and possibly for Y and dY.
(The TAB key moves the cursor through the blanks in the order: X, dX, Y,
dY).
Click on
the button for the desired operation or function.
The equation for
the calculation appears in the central blank, and the values of Z and dZ
appear in their respective blanks.
There are
buttons for transferring values from Z to a MEMory location, or to the
blanks for X or Y; or from the MEMory to X or Y.