Here's an interesting Pre-TNG look at Warp drive
Introduction to Navigation
Star Fleet Command Technical Publications Section (c) 1980
Section 1.3 Warp Speeds
As Zefram Cochrane pointed out in 2053, actual warp speeds relative to the speed of light may be calculated by multiplying the warp factor cubed by a variable that acounts for the curvature of space in a fourth dimension by the presence of mass; subspace, a continuum in which a vessel under warp drive travels, is not curved in a fourth dimension, and therefore offers a linear "shortcut" between points in our galaxy. This variable, called Cochrane's factor, and sometimes indicated by the greek letter chi, can be as high as 1,500 in dense dust and gas clouds and as little as 1 in the intergalactic void. It is larger near massive objects such as stars and black holes, as space is curved around such objects to an even greater extent. For practical reasons, warp drive is not used in the vicinity of massive objects, as the disproportionately high warp speeds tend to produce a "slingshot effect," catapulting a starship out of the space-time continuum altogether. Between galaxies, where negligible matter exists, space is not perceptibly curved, and the short cut afforded by Cochrane's factor dissapears. Warp speeds attain their "ideal" (Wf3 x c = v) values, and the transit time to the Andromeda galaxy becomes thousands rather than hundreds of years.
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Later on they give the chi value as being 1292.7238 as being the average value of Cochrane's factor within Federation Space.
The book is really an interesting read. it goes on to describe arrival and departure regulations in regards to entering a busy star system. Also lists planets mentioned or visited by the Enterprise during her three years on the air. Included with the book was two poster size star charts with charts front and back. Highlights include the Romulan Neutral Zone, last known locations of lost starships Intrepid, Constellation, Valiant, Archon, and Defiant. The paths of Rejac, Nomad, and the Botany Bay. Also included, is the borders of the Tholian Assembly, Klingon Empire, Romulan Empire, and the Kzinti Patriarchy.