The standard data processing (SDP) of Chandra data is divided into several stages or "Levels" (see the level ahelp page). At the end of each level a well defined set of data products are made, and these form the basis for the next level of processing.

L0

takes raw Chandra spacecraft telemetry and splits it into convenient FITS files.

L0.5

divides the telemetry on observation boundaries.

L1

applies instrument corrections to produce "event files" with aspect corrected positions for each event.

L1.5

(only for grating data) uses the position of the zeroth-order image to produce corrected positions for the dispersed counts (which can only be identified at this level). This removes blurring due to rotation.

L2

filters the event file to good time intervals (GTI), produces a candidate source list, and - if a grating observation - extracts a dispersed spectrum.

L

consists of catalogs and aggregate analysis of large numbers of observations. An example of a level 3 product would be a Chandra Source Catalog for all non-proprietary data, with sources identified and cross referenced with other catalogs. To date, there have been no L3 products created.