Part 1: General This information 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 ... To continue reading, start your free trial here. Please note your trial does not include access to downloads. To explore our subscription options and access downloads, please click here. Or sign up to the isurv newsletter, your monthly round up of the latest isurv updates. For further questions, don't hesitate to call: +44(0)247 686 8555.