At least this is what the MassLib user finds on the respective menu item. 
MassLib features more instead: Background corrections and the automatic determination of unique ions are so frequently used they got implemented as permanent buttons (BCorrect) or as a standard tool (Unique Ions and 
Check) also appearing on Curve and Spectra popup menues. Peakfinder, a tool allowing semiautomatic SISCOM searches is of a similar nature (tool button, Curve menu entry).

• GC/MS Background Correction: The most important and also most frequently used arithmetic feature of MassLib is its automatic background correction for GC/MS (neither broad peaks nor very low intensities nor non-GC runs such as solid probe work are covered by this practical tool). BCorrect is very conservative and does corrections on each mass trace individually (it is no spectrum subtract algorithm).

• Unique Ions: For all kinds of mixture corrections and quantitative considerations concerning overlapping peaks, unique ion traces (mass traces of ions unique to only one of the overlapping components) are essential. MassLib finds them itself (tools Unique Ions and Check). The tool is insensitive towards GC/MS column bleed fluctuations. How important this tool is to find components buried in the background or in coelutions, or hidden in flat TIC-controlled solid probe analyses is evident. 

• Peakfinder: Working on a selection of e.g. a GC/MS run it finds the most important spectra itself for further processing such as SISCOM searches. Once initiated the MassLib user is set free for a coffee break or for more demanding tasks. Output redirection to the printer allows him to look over the results very quickly as the structure plots on the output will give him the clues where to continue work interactively. Output may contain a hitlist of spectra with structures as well as the unique ion Check described above.

• Arithmetics: Even if background corrections are mostly done on each spectrum it is sometimes desirable to add spectra first und then subtract some summed up background. MassLib facilitates the operation by filling in the selected spectra automatically in the arithmetics window and by offering Add Spectra on a selection popup menu. Additions and subtractions may either be done by mean value or by an explicitly given percentage.

Spectrum corrections (to account for overlaps) is another important issue. Rarely the arithmetics window is used for this as the spectrum popup menu offers both, automatic corrections and corrections by zeroing unique ions (defined simply by positionning the mouse on the unique ion’s mass trace).

• Quantitation: MassLib does not yet provide quantitation for GC/MS work. An according module is planned however. Currently available and implemented into the calculations menu is a tool allowing to fit a given set of spectra (such as a part of a hitlist) into a spectrum. The goal is to find the percentage of each component in a mixture. Similarly, using unique ion traces as the representatives of overlapping components, a fit of the unique ions curves into the RIC (Reconstructed total Ion Chromatogram) allows an estimation of the percentage each component contained in a mixture GC peak represents.

• Isotopic Patterns: A flexible module does not just allow to calculate simple isotopic patterns but to generate also complex isotopic clusters (created by e.g. variable amounts of hydrogen loss). The feature may also be used (using the Compare spectrum display) to check isotopic patterns in unknowns.