Caving Canada Canada’s Longest  Caves Background Info
There are a few bits of information to keep in mind when trying to interpret the tables in these pages. 
Abbreviations     Newsletters and Magazines IU Island Underground VN VICEG News JSM Journal of Subterranean Metaphysics CC Canadian Caver CC-CEC Canadian Caver Special Issue - Cave Exploration in Canada (1976) BCC BC Caver      Books UGM Under Grotto Mountain. Chas Yonge 2001 CCR Caves of the Canadian Rockies and Columbia Mountains. Rollins 2004   Survey Information        It’s important to remember that many of the longer cave surveys are works in progress, and the       current length and/or depth will change in time. The lengths or depths for caves in progress are       reported from a person holding the survey data. Survey Accuracy       Cave surveying is conducted using some device to measure distances between survey stations,       some way to measure direction (either relative or absolute), and, ideally, some way to measure       difference in elevation. How this is done covers a spectrum of accuracy, from crude and quick to       laborious and (hopefully) accurate.             Most cave surveys in Canada use a fibreglass tape measured to the nearest centimetre,       a Suunto sighting compass for bearings, and a Suunto clinometer for angles between stations.       Usually, the passage dimensions are estimated and a sketch created in a notebook onsite.       Here’s a general grading system for cave surveys, from the International Union of Speleology        Have a look at the source link for more information.       
Grade 	Description   -1 		no map available   0 		ungraded   1 		Sketch from memory, not to scale   2 		Map compiled from annotations, sketches and estimates made in the cave.  No instruments used.  3 		Directions measured by compass, distances measured by cord pace, or  body dimensions. Significant slopes estimated.  4 		Compass and tape survey, using deliberately chosen and fixed stations.  Slopes measured by clinometer or horizontal and vertical components of line.  5 		Compass and tape survey. Directions and slope by calibrated instruments,  distances by fibreglass or metallic tape, or tacheometry.  6 		Survey or triangulation using calibrated, tripod-mounted instruments for  directions and slope. Distances by calibrated tape, precise tacheometry,  or calibrated DistoX type.  X 		Survey by theodolite or comparable means
Lengths and Depths? Cave depths are the vertical distance between the very highest part of a cave system to the very lowest point. Often the highest point will be the edge of the entrance sinkhole, though, this varies considerably depending on the “keenness” of the survey crew. Even the lowest point can change somewhat, since if it is a sump (point that is waterfilled) this could vary with season or be completely bypassed by cave divers. Cave lengths very often depend on a both a combination of the actual extent of the cave and the enthusiasm of the mappers. Surveyors mapping for the main passages and just sketching minor side-passages will end up with a published cave length far less than the meticulous crew who drag a tape into every nook and cranny.