CIRAS-3 Operation Manual V. 1.09  147  support@ppsystems.com 
 
Do I Use Linear versus Quadratic 
The CIRAS-3 system automatically collects data based on both a linear or quadratic fit for the assimilation 
data.  In the past quadratic fitting was most popular but at the request of some customers we have now 
also introduced a linear fitting.  As discussed in the theory section, on theoretical grounds, the relationship 
is likely to deviate from a linear response, especially at high assimilation rates.  Generally speaking, if 
your rates are low we recommend using the linear fit.  For most measurements with higher rates the 
quadratic fit is normally recommended. 
 
Closed System Operation 
Many of the features related to closed system measurement screens (numerical and graphical 
presentation of data, graph set, recording measurements, etc.) are similar to what has already been 
discussed in this operation manual.  The displays are also similar when using the SRC-1 / SRC-2 Soil 
Respiration Chamber or CPY-4 / CPY-5 Canopy Assimilation Chamber. 
Numerical Data Display (SRC-1 and SRC-2)