﻿ Math calculators
 Basic math calculators
The SPECIAL menu contains several utility routines useful in respirometry (STP conversion, altitude and pressure calculations, a metabolism estimates routine, a routine to compute ventilation) and a simple calculator.   For convenience they can be activated from the main plot window by typing specific keys, indicated by ‘key’ on the menu.

•   SIMPLE MATH CALCULATOR...     This is an elementary math calculator (addition, subtraction, multiplication, division) with a few frequently-used functions (logs, square roots, etc.) and some specialized keys for interchanging time units (division and multiplication by 60 and 24).  If you have obtained a mean value with an ANALYZE menu operation, you can transfer that mean to the calculator for additional manipulation (note that this does not work for regression slopes).  The 'store X value...' button lets you save the result for use as a scaling factor in subsequent ANALYZE operations.  Clicking this button opens the scaling factors window.  Click on any channel's "*" or "÷" button, and the current X-value will appear in the first edit field (the multiplication or division factor) for that channel.

• The initial X value will be set to the last computed value obtained from several of the calculators (STP, metabolism, etc.).   If no such value is available (i.e., no calculators have been used), the initial X value is set to 1.0.

• Mathematically impossible operations (such as attempting to take the square root of a negative number) will generate a warning notice (this calculator only deals with real numbers).

 For addition, subtraction, multiplication, and division the calculator works in a simple RPN mode.  Enter the first number in the X-value edit field, hit 'return' and enter the second number, and then hit the '+', '-', '*', or '/ ' key.  Note that for performing subtraction in RPN, the ‘_’ (underline) key is substituted for the '-' (minus) key.    The result appears in the X-value field. Also note that when computing sines, cosines, or tangents, the calculator expects angles in degrees (not radians).

•   SIMPLE REGRESSION... 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).

• The 'Save Data…' button saves the current X and Y values to an Excel-format text file (this button is not available until you have calculated at least one regression).