Regularly cleaning under a car is essential, especially after the winter, to prevent collected salt and other muddy deposits from promoting rust.
The process usually involves a high pressure spray being poked about under the wheel arches and various other nooks and cranies, along with a fair bit of groveling around to try and see if there are any stubborn bits clinging on, in the face of the watery onslought.
These clingers are difficult to see, because the underseal is always black, i.e. the same colour as the reluctant detritus, but this problem is now solved with the introduction of The Chassis Graph.
If you choose to have The Chassis Graph treatment applied to the underside of your car, before it's delivered, its weather-proof coating will be white instead of black, and have a series of thin blue lines sprayed unto it. These lines run at right angles to each other in both directions to create the pattern of a graph the covers the entire underbody of the car.
With your Chassis Graph in place, cleaning now becomes a simple matter of spraying away until the lines clearly reveal themselves against the white background.-- xenzag, Apr 07 2009 Kind of a "cleaning between the lines" kind of thing ... [+]-- Aristotle, Apr 07 2009 Or a Monocoque Monograph for more up-to-date motors?-- coprocephalous, Apr 07 2009 [+] but I'm not sure why the blue lines are necessary. is the reluctant detritus ever white?-- Srimech, Apr 07 2009 //but I'm not sure why the blue lines are necessary// Well, large areas of the underside of a car are fairly nondescript. With a graph in place, individual cells can have a numerical grid value for greater clarity in the need for future reference.
eg "I was servicing your car, and I noticed a rust spot on one of your brake pipes" - "Oh yea - where exactly?" "At the intersection of 16r + 22f"-- xenzag, Apr 07 2009 Clean the underside, lend the car to the kids and read off the dirt graph of how the car was driven.-- wjt, Apr 07 2009 What size grid scale do you have in mind?-- tatterdemalion, Apr 08 2009 In a high salt area, having some contrast would be a good thing.-- MechE, Apr 08 2009 random, halfbakery