This experiment was the 4th analysis of a drilled sample from Mars. It
is known as John Klein 4. It revealed the continued presence of the
derivatization reagent, N-methyl-N-tert-butyldimethylsilyl-
trifluoroacetamide (MTBSTFA), in the sampling handling system. 
For estimation of abundances of volatile compounds detected in EGA,
the background was subtracted as a constant value, typically early
in the run. Exceptions to this were O2 and CO2, for which the
background was modeled as trending downward during the run.
Uncertainties in abundances, deriving from statistical noise,
background subtraction, calibration factors, assumptions regarding
ionization cross-sections for the relevant compounds, and isobaric
interferences, are estimated at 10-20% of the values.