NIST (National Institute of Standard and Technology Guide for the use of the International System of Units (SI) - Acrobat PDF file

International System of Units from NIST

Bureau International des Poids et Mesures(BIPM)

British Standards Online

European Pressure Equipment Directive (PED)

Society for Piping Engineers and Designers (SPED)

On Line Unit Converters

Rigzone Oil & Gas Conversion Calculator

Conversion & Calculation Centre (weighing-systems.com)

http://www.encyclopedia.com/

http://www.dictionary.com/

http://www.thesaurus.com/

Encarta Online

britannica.com

MatWeb, Your Source for Materials Information

Piping Design Central

Engineering Toolbox