Keywords: class-evol1

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## Contents

- CLASS internal data format
  - Pointed observation
  - On-The-Fly observation
- Limitations, ease of use and efficiency
  - Philosophy
  - Implications
  - Warning
- Large dataset processing
  - Basic idea
  - Listing and Table of Content
  - Index consistency
  - Visualization
  - Sorting
  - Baseline fitting
  - Interactive data exploration
- Miscellaneous changes
  - New defaults
  - Command names
  - Griding and spectra cube visualization
  - PLAIT algorithm
- CLASS90 for beta testers

### Abstract:

CLASS is a GILDAS1 software for reduction and analysis of (sub)-millimeter spectroscopic data. It is daily used to reduce spectra acquired with the IRAM 30m telescope. CLASS is currently used in many other facilities (e.g. CSO, HHT, Effelsberg) and it is considered for use by Herschel/HIFI. CLASS history started in 1983. As a consequence, it was written in FORTRAN 77 and tailored to reduce pointed observations. On-The-Fly support was added in the 90s but it showed limitation as the quantity of OTF data increased quickly. One year ago, we decided to fully rewrite CLASS in FORTRAN 90 with the 3 following goals: 1) clarifying satisfying features with backward compatibility in mind, 2) improving code readability to simplify maintenance and 3) easing reduction of large OTF data sets. This memo is describing the current state of affair with a particular emphasis on changes in the program behavior. Future foreseen changes (linked to the increase of receiver instantaneous bandwidth like an improved conversion from frequency to velocity axis) will be described in a future memo.