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•   SIMPLE MATH calculator This is a basic calculator with some additional keys that are specific to data acquisition.  Along with standard math operations, it contains keys for a number of surface and volume conversions frequently used by physiologists and other scientists.

The calculator has an RPN function with addition, subtraction, multiplication, and division (which should be familiar to users of HP desk calculators).   Note that you should use the underline key (_) instead of the minus key (-) for subtraction (this is because the minus key is assumed to indicate a negative number, not subtraction).

Also note that when computing sines, cosines, or tangents, the calculator expects angles in degrees (not radians).

•   SIMPLE REGRESSION calculator This window lets you perform simple linear or 2-order polynomial regressions.   It is not intended to replace the much more sophisticated regression algorithms found in dedicated statistics packages:   it doesn't provide a lot of the standard regression statistics, and there is an upper limit of 20 X-Y variable pairs (you need to enter at least three).   Once the data are entered, clicking the 'Calculate Regression' button computes and displays the regression coefficients and shows a plot of the data and regression line:

• Once a regression has been computed, you can use the 'Predict Y from X' and 'Predict X from Y' buttons to interpolate values (but note that predicting X from Y does not always work in polynomial regressions).

• The X and Y values will be remembered if you close this window and subsequently re-open it (but are lost when you quit LabAnalyst).

•   EXPRESSION EVALUATOR This routine lets you write a mathematical expression, enter numeric values for the expression variables, and have the computer solve it. The program parses the expression into components and performs the operations. The expression evaluator understands the following symbols (upper or lower case entries are OK):

• Simple operators: + - * / ^ ( )
• Complex operators: EXP, LOG or LN, LOG10, SIN, COS, TAN, ATN or ATAN, ABS, INT, SQR (square), SQRT (square root)
• Two special variables (i.e., channels) named "X" and "Y", chosen with push-buttons (see image below)
• PI (or the equivalent Greek letter)
• Numbers (such as 5, -3.1889, and 1e-10)
• You can add a comment at the end of your expression, delineated with the " ` " character.

Some general considerations:

• The 'Check expression' button does a preliminary parsing of the expression and indicates if there are any syntax errors (in the above example, this button has been clicked).
• The 'Evaluate' button processes the X and Y values according to the expression in the upper left window. Results are shown in the yellow text box at the bottom of the window. If any errors are found (see below), a warming message is shown.

NOTE: This routine will only 'catch' errors in the basic numeric expression. It may not detect invalid or meaningless math operations that may be attempted when data are processed, such as division by zero, or taking the log or a non-integer exponent of a negative number. If such situations occur, results may be unpredictable. The algorithm does find most such errors during processing, however.

 The underlying code for the expression evaluator was developed by the late, great Robert Purves (recently deceased and greatly missed).  I 'borrowed' it -- with his permission -- and made some modifications for LabHelper.  But Robert P. deserves all the credit.

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