Part 1: General This document is only available to paying isurv subscribers. Symbols, abbreviations and certain key words and phrases used in the rules are as detailed below. 1.6.1 Symbols used for measurement ft2 ... Sign up for a free trial here. Please note that the free trial does not include access to downloads. Or sign up to the isurv bulletin, our monthly newsletter detailing the latest content on isurv. For further questions, don't hesitate to call: +44(0)247 686 8555.