Calculators ('Help' menu)

Simple math

STP adjustment

Altitude & pressure

Flow rate estimates

  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). 

Note that 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.  The result will appear in the X-value field.

   STP ADJUSTMENT   This small calculator is used for adjusting a measured flow rate to conditions of standard temperature and pressure (STP).  STP conversion is necessary for gas exchange calculations. 

• You can select either a measure of uncorrected flow rate (in ml/min) or a cumulative volume (ml) over a measured time period (seconds).  The latter method is most useful for dry volume meters, bubble meters, etc. 
• In addition to barometric pressure, you can account for any internal pressure within the gas flow meter (which may occur if you are using relatively high flow rates and/or small-diameter tubing).  Internal pressure can be in units of torr, PSI (pounds/square inch), KPa (Kilopascals), or mm of water (if you are using a water manometer). 
• You can adjust the calibration temperature of your flow instrument.  Most such devices are calibrated for a temperature of zero °C, but some (like Singer dry volume meters) may be calibrated for 20 °C or other temperatures. 
• The 'sigma' button adds the current value into an internal register that is used to compute an average value (displayed with the 'show average' button).  These functions correctly account for whether the display is set for standard cubic centimeters/min (SCCM) or standard liters per minute (SLPM). 
• The 'store' button saves the current flowrate (and also sets pressure and temperature to STP conditions -- 760 torr and 0 °C)

  ALTITUDE & PRESSURE     This option computes an estimate of mean atmospheric pressure as a function of altitude, or vice versa.  It is based on the International Standard Atmosphere, obtained from the Smithsonian Meteorological Tables. (as a rough approximation, pressure decreases by 50% for every 5500 meter increase in altitude).  The results should be accurate within 1-2% of actual pressure or altitude, unless weather conditions are really unusual.  Nevertheless, you need to keep a few caveats in mind:

• Due to approximation (and rounding errors), the algorithm is not completely reversible (for example, the estimated pressure for an altitude of 2200 meters is 581 torr, but the estimated altitude for a pressure of 581 torr is 2204 meters). 
• The results are estimated mean values and do not account for local pressure fluctuations arising from weather changes. 
• The calculator cannot account for any pressure differential inside your system.  For example, if you use a positive-pressure ("push") respirometry system, the pressure inside the plumbing -- and hence, inside your flow meter -- will be slightly higher than atmospheric.  The opposite is true for a negative-pressure ("pull") flow arrangement.  If you want to be compulsive, you might consider using a water manometer or some other pressure gauge to measure the pressure differential and add that to atmospheric pressure during STP calculations. 
• Accuracy will decrease for altitudes above about 9000 meters (or pressures less than about 230 torr).
• The 'store pressure' button will save the current value of barometric pressure.
• The latest versions allow a choice (kilopascals or torr) for pressure units.

   The FLOW RATE CALCULATOR estimates metabolic rate based on size, phylogeny, temperature, and activity. From the estimated metabolism and a user-set limit on the amount of oxygen deflection, LabHelper computes the minimum necessary gas flow rate in an open-circuit respirometer.

In this example, the subject is a nestling bird weighing 12.52 grams. The allometric equation for nestling resting metabolic rate (RMR) is shown and the variables (mass coefficient and mass exponent) can be adjusted as desired (this particular equation is from Weathers & Siegel, 1994). Activity level can be set at minimal metabolic rate (MMR) or several exercise intensities up to 100 X MMR (probably only relevant for flying insects).

When working with fish, the program switches from changes in oxygen concentration to changes in percent oxygen saturation. It calculates the oxygen content of water from temperature and salinity; you can select three different salinity levels (fresh, brackish, and salt water) to compensate for the effects of solutes on oxygen content.

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