Fitting tools vs sales tools
Bike fitters have a lot of special tools to do their job. Some I would call fitting tools, most are really sales tools. There is a clear distinction between the two. Things that group humans by some measurement to sell a specific product are sales tools. A good example would be the Specialized sit bone measuring device (A.K.A. the ass-o-meter). It tells you if you need a 143, 155 or 168 saddle, as if saddle width was the only parameter. Things that measure biodiversity are fitting tools. It's much harder to give an example of a bike fitting tool because bike fitting has become all about sales. The best example I can think of would be the Rotational Angle Device pedals. RAD pedals are just free floating pedals with indicators sticking out the side. They accurately tell the fitter which way the rider's foot points as they pedal. They were a product of the New England Cycling Academy in the 1970's - yes, it's 50 year old technology. It's very simple technology, it's a measuring device for dynamic foot angle, yet nobody else uses it. Every other fitter claims to be able to set up cleats without this measuring device, I don't know how. I do get a lot of clients who have had cleats adjusted by other fitters, but still have problems as they pedal. I put them on the RAD pedals and see that they are way off. The bottom line: If there is a measuring tool that shows information needed to do the job, use it...
This brings up the argument about measuring device vs. the human eye. Computer based fitting systems use measuring devices to make a digital model of the rider on the bike. They show accurate numbers of joint angles and relative positions which I couldn't even come close to. I would be better off with some sort of digital tracking system, it would certainly make documenting a position or tracking changes over time better. The problem is that people don't understand how to use the data from these systems. Most clients get one Retul fitting, and they're happy because they have data. They don't own a method of getting those numbers themselves, so the numbers they got from the fitting are pointless. Within the fitting process that data could be very useful in problem solving, but I think their accuracy is a bit of overkill when applied to the human body. I have mechanical methods to measure what I need to measure, I come up with measuring tools when I need them.
If I have one true complaint about digital fitting systems it's that they ignore the response of the human body. In setting saddle height they take femur, tibia and foot lengths and compare them to similar cases within their database. In contrast Steve Hogg has an explanation of saddle height limit based on two muscles. The quad muscles extend the lower leg from the knee, the hamstrings close the knee angle. The connective tissue of the quad goes over the knee and attaches at the tibia while the hamstring takes a straighter line. When the knee is bent both muscles have mechanical advantage. As the leg straightens out the hamstring loses mechanical advantage as the angle approaches zero. The quad still has mechanical advantage because the knee acts as a raised fulcrum. The knee is no longer a balanced pivot - the saddle is too high. Digital fitting systems have the raw data to see this, they just don't know how to use it. They can estimate muscle attachment points, they can calculate mechanical advantage of both the quad and hamstring. They don't because it's hard to explain this to people. Anything that uses a simple explanation over a good method is a sales tool.