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R, 18th letter of the alphabet, corresponding to Greek rho. When in Latin alphabets the letters for p and r became similar in appearance, the rho form (P; which at first was used for the r sound) was restricted to the p sound, and an extra line was added for the r sound (R). In Greek, where no confusion developed, the rho continued to look like Latin P. A modification of R is the symbol ℞, used medically for recipe [Lat.,=take] and liturgically for responsum [Lat.,=response].
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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
1. Abbr. for “radius.”
2. Abbr. for “right.”
3. Symbol for the capacity of a pile (for example, 3R indicates three times design capacity).
4. Symbol for the thermal resistance of a material or component of construction.
5. Symbol for electrical resistance.
sound reduction index, R
British term for sound transmission loss.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
RA programming language for statistical computing and graphics that is released under the GNU license. R was designed to handle a wide variety of complex statistical tasks, and many user-developed routines are also available. R is the open source version of S, which was developed in the mid-1970s by John Chambers at Bell Labs (S-PLUS was a commercial version from TIBCO Software). For more information, visit www.r-project.org.
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