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The Precision Measuring Machine (PMM)

The Precision Measuring Machine (PMM)

The Precision Measuring Machine (PMM), is a large, fast, highly precise custom built photographic plate measuring engine. The goal of the PMM Project is to produce stellar catalogs which are both deep and dense, based on digitization of the major photographic surveys. The latest catalogs, are USNO-B1.0 and USNO-A2.0.  A short graphical summary of the operation of the PMM and how astronomical photographs become star catalogs is given in PMM Operations (file format: PDF, size 3.5MB).

The Precision Measuring Machine is housed in a clean room at the USNO Flagstaff Station. It was built by Anorad, Inc. of New York.  The base of this machine is a single block of granite weighing roughly 10 tons which rests on a concrete pier that is isolated from the floor of the room to prevent vibration of the measuring machine. Twin CCD (charge coupled device) cameras are set up to "fly" a constant distance above the photographic plates, stopping every few seconds to take digital "snapshots" of a small area of the photographs. The platen rest on a horizontal platen, which is in turn supported by four air bearings which float on a thin cushion of air above the granite base. These air bearings further isolate the photographic plates from vibration and insure that they move very smoothly while being digitized.

The images taken by the CCD cameras are measured and analyzed while the plates are still being digitized, so positions and magnitudes of all the stars have been computed by the time a plate has been scanned, usually in less than an hour for each plate. The measuring and analysis time varies depending on the number of stars on the plate. Photographs taken in and near the plane of the Milky Way galaxy have so many stars on them, they appear almost black, and these plates can take several hours to measure.

The PMM Project Read Me Files

These are files that were included on the USNO-A1 and -A2 distribution CD-ROMs and contain explanatory information that is relevant to understanding the data imaged by the PMM. In order to allow for updates to the text, information on problems or improvements, and to provide additional instructions, the latest versions of the files are displayed here. These files should always supercede those on the CD-ROM. Check the dates on the files; note that the latest CD-ROM is dated September 1998. Updated files will be marked as such.

  • Introduction to USNO-A2.0 (README.V20)
  • Introduction to USNO-A1.0 (README.V10)
  • Discussion of the USNO-A1.0 astrometry (READ.AST).  There was no update for USNO-A2.0.
  • Discussion of the USNO-A1.0 photometry (READ.PHT).  There was no update for USNO-A2.0.
  • Discussion of the PMM design, hardware, and software (READ.PMM).
  • How to read the USNO-A2.0 (READUSE.V20)


How did the PMM turn photographs into star catalogs?
See this poster on the operation of the PMM (File Format: PDF, Size: 3.5 MBytes).
What is the correct citation for USNO-B1.0?
Monet, D. G. et al. 2003, "The USNO-B Catalog", AJ, 125, 984 (File Format: PDF, Size: 0.3 MBytes).
What is the correct citation for USNO-A2.0 or -SA2.0?
You should check with the editor of the publication for which you are preparing your article, but we suggest treating the catalog like a book, and using that sort of a format. For many publications, the following is appropriate. The author string can be found in README, and the USNO-DC library has an archival copy should Flagstaff get nuked.
Monet, D., Bird A., Canzian, B., Dahn, C., Guetter, H., Harris, H., Henden, A., 
Levine, S., Luginbuhl, C., Monet, A. K. B., Rhodes, A., Riepe, B., Sell, S., 
Stone, R., Vrba, F., & Walker, R. 1998, 
The USNO-A2.0 Catalogue, (U.S. Naval Observatory, Washington DC).
What is the correct citation for USNO-A1.0 or -SA1.0?
Monet, D., Bird, A., Canzian, B., Harris, H., Reid, N., Rhodes, A., Sell, S., 
Ables, H., Dahn, C., Guetter, H., Henden, A., Leggett, S., Levison, H., 
Luginbuhl, C., Martini, J., Monet, A., Pier, J., Riepe, B., Stone, R., Vrba,F.,
Walker, R. 1996, 
USNO-SA1.0, (U.S. Naval Observatory, Washington DC).