Lettering standards

TABLE 2.6 Abbreviations and Standard Letter Symbols Continued)... 

So basic is the notion of a statistical estimate of a physical parameter that statisticians use Greek letters for the parameters and Latin letters for the estimates. For many purposes, one uses the variance, which for the sample is s and for the entire populations is cr. The variance s of a finite sample is an unbiased estimate of cr, whereas the standard deviation 5- is not an unbiased estimate of cr. 

The list given below includes the substances that are most used and most useful for the standardization of solutions for precipitation titrations. Primary standard solutions are denoted by the letter (P) in Column 1. 

Section 2 combines the former separate section on Mathematics with the material involving General Information and Conversion Tables. The fundamental physical constants reflect values recommended in 1986. Physical and chemical symbols and definitions have undergone extensive revision and expansion. Presented in 14 categories, the entries follow recommendations published in 1988 by the lUPAC. The table of abbreviations and standard letter symbols provides, in a sense, an alphabetical index to the foregoing tables. The table of conversion factors has been modified in view of recent data and inclusion of SI units cross-entries for archaic or unusual entries have been curtailed. 

A.STM. Standardisation Nem (formerly Materials Kesearch and Standards and, earlier, A.STM bulletin) American Society for Testing and Materials A monthly bulletin which covers ASTM projects, national and international activities affecting ASTM, reports of new relevant technology, and ASTM letter ballots on proposed standards. 

Viscosity can also be determined from the rising rate of an air bubble through a Hquid. This simple technique is widely used for routine viscosity measurements of Newtonian fluids. A bubble tube viscometer consists of a glass tube of a certain size to which Hquid is added until a small air space remains at the top. The tube is then capped. When it is inverted, the air bubble rises through the Hquid. The rise time in seconds may be taken as a measure of viscosity, or an approximate viscosity in mm /s may be calculated from it. In an older method that is commonly used, the rate of rise is matched to that of a member of a series of standards, eg, with that of the Gardner-Holdt bubble tubes. Unfortunately, this technique employs a nonlinear scale of letter designations and may be difficult to interpret. 

TEMA Numbering and Type Designation Recommended practice for the designation of TEMA-style shell-and-tube heat exchangers by numbers and letters has been established by the Tubular Exchanger Manufacturers Association (TEMA). This information from the sixth edition of the TEMA Standards is reproduced in the following paragraphs. 

This defines the maximum permissible composite error at the rated accuracy limit primary current, followed by letter P for protection. The standard prescribed accuracy... 

The Tubular Exchanger Manufacturers Assn, has established heat exchanger standards and nomenclature. Every shell-and-tube device has a three-letter designation the letters refer to the specific type of stationary head at the front end, the shell type, and the rear-end head type, respectively (a fully illustrated description can be found in the TEMA standards). Common TEMA designations are listed with specific configurations described below. 

The required notification must be provided at ieast annually In writing. Acceptable forms of notice are, for example, a letter, product labeling, and product literature distributed to customers. If you are required to prepare and distribute a Material Safety Data Sheet (MSDS) for the mixture under the Occupational Safety and Health Act (OSHA) Hazard Communication Standard, your section 313 notification may be attached to the MSDS or the MSDS may be modified to include the required information. (A sample letter and recommended text for inclusion in an MSDS appear on pages E-4 and E-5 of this appendix.)... 

The term issue in the context of documents means that copies of the document are distributed. You will of course wish to issue draft documents for comment but obviously they cannot be reviewed and approved beforehand. The sole purpose of issuing draft documents is to solicit comments. The requirement should be that the documents are reviewed and approved prior to use. Some organizations insist that even drafts are approved for issue. Others go further and insist that copies cannot be taken from unapproved documents. This is nonsense and not what is intended by the standard. Your draft documents need to look different from the approved versions either by using letter issue notation (a common convention) or by printing on colored or watermark paper. If the approved document would carry signatures, the absence of any signature indicates that the document is not approved. 

To aid in readability by plant management as well as engineering and operating personnel, it is important that a set of symbols be developed as somewhat standard for a particular plant or company. Of course, these can be improved and modified with time and as needed, but with the basic forms and letters established, the sheets can be quite valuable. Many companies consider their flowsheets quite confidential since they contain the majority of key processing information, even if in summary form. 

Note that in Figure 6-8 and Table 6-2 the letter designations of the stages conform to the latest Standards of the Heal Exchange Institute for Steam fet Vacuum Systems [11]. The letter designates the jet s stage position in the system. 

Eigures 10-lA-G and Table 10-1 from the Standards of Tubular Exchanger Manufacturers Association give the nomenclature of the basic types of units. Note the nomenclature type designation code letters immediately below each illustration. These codes are assembled from Table 10-1 and Eigures 10-lA-G. 

Pascal names (of units, variables, array elements, etc.), consisting of an initial letter followed by letters or digits, may be as long as needed in standard Pascal however, in practice, most compilers require that a name be unique within a certain number of characters. (See Table 1-28 for reserved words which may not be used as names.)... 

In 1987, I ADC developed a revised standard nomenclature for roller bits which includes a classification chart and a four-character bit code. All manufacturers must classify their bits in a prescribed manner on the lADC classification chart. The classification includes four categories series, types, feature, and additional features. Figure 4-136 shows an lADC classification chart. A letter used in the fourth position of the four-character lADC code indicates additional design features specified in Table 4-91. 

Most standard forms of contract contain specific procedures for determination, and these should be rigidly adhered to. For example, the contract document may lay down that the contractor be given 14 days notice in writing to rectify his progress before determination is carried out. Any letters should be sent by recorded delivery or served by hand. While liquidated or non-liquidated damages can be claimed with respect to late or incomplete work, expense claims usually follow the events shown below, which are also mentioned in Section 8.24 ... 

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