Subject: BUNIT names for dimensionless numbers?

From: Jeff Bloch <jbloch at sstcx1.lanl.gov>
Date: Sun, 15 Jan 1995 17:44:21 -0700 (MST)

I have read over the OGIP Memo on physical unit names for the BUNIT 
keyword. My question is what is the preferred way unitless 
numbers like standard deviations, or dimensionless ratios should be 
labeled in the BUNIT parameter?

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Jeffrey Bloch					Office:     (505) 665-2568
Astrophysics and Radiation Measurements Group	ALEXIS Soc: (505) 665-5975
Los Alamos National Laboratory			FAX:	    (505) 665-4414
Group NIS-2, Mail Stop D436			e-mail:	    jbloch at lanl.gov
Los Alamos, NM 87545
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From: "Ian M George, Code 668, NASA/GSFC, USA (Usque ad mortem bibendum)" <GEORGE at lheavx.gsfc.nasa.gov>
Date: Thu, 19 Jan 1995 19:12:10 -0500 (EST)

> labeled in the BUNIT parameter?

... As Jeff correctly points out, the memo (OGIP/93-001) concerning
the OGIP-approved character strings used to specify physical units 
(currently) does not mention what to do in cases where the physical 
quantities are dimensionless. 

... In such cases, I believe most OGIP-produced files are currently 
using a "blank" character string (ie padded with spaces) as the keyword 
value. However, I admit that this may not be the best choice since it 
is ambiguous as to whether the associated physical values really are
dimensionless, or whether the creator (human or s/w) simply forgot to 
construct & fill in the appropriate string.

... To this end, I would be interested in getting feedback on the 
following proposed addendum to the current memo:
|                                                                     |
|   a)  - If the physical quantity is dimensionless,                  |
|           then the string 'unitless' be used                        |
|   b)  - If the units of the physical quantity are unknown,          |
|           then the string 'unknown' be used                         |
|                                                                     |
|   In both cases, the strings should be considered case-sensitive    |
|                                                                     |
|   A "unit-string" consisting entirely of spaces should also be      |
|     considered to imply that the associated physical quality is     |
|     dimensionless.                                                  |
|                                                                     |
... Please post any comments to this newsgroup asap. Finally I'd like to 
emphasise that this is personal response to the question, and has not 
yet been discussed by the OGIP FITS Working Group.

Regards
Ian M George
HEASARC