http://www.oriold.unizh.ch//static/hegira.html

Date conversion

http://www.filatelia.fi/experts/

Experts

http://www.wnsstamps.ch

WADP Numbering System - WNS

http://www.arabianstamps.com

Good information on Saudi new issues

http://www.stamps.org

American Philatelic Society

OPAL home page

OPAL

http://www.filatelia.fi/experts/

Royal Philatelic Society London