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The final issue has to do the question of how similar or applicable it is it to model and compare the dynamic rod flexion configuration in an actual cast versus reproducing that rod flexion profile in a static state by positioning the rod horizontally and hanging a weight on the tip. That is a very complex question. I am simply going to state that others, such as Bolton, have done so and suggested that it is valid, if not precise. The fact it that it is so simple to do so, and so intuitive, one can hope there is some fairly linear proportionality in comparing a Force of weight hanging on a static rod tip to a given flexion to the Force applied in the hand, or calculated at the rod tip by actual acceleration measurements (high speed pictures) to produce the same flexion.

And note, in a model, precision, validity, and utility are three separate issues. One could hope for all three. But the most important is utility. This model is to be used and applied by laymen. Precision demands complexity and that reduces utility. The ability of the model to predict rod behavior in a useful fashion will itself predict validity.

V The Predictive Model

I decided to present the guts of the model at this point since discussion of the haul will distract from the connection with the previous discussion and the model itself.

So far the model, with the exception of introducing the rod-as-rigid-lever concept is just repeating common and accepted models of the casting stroke. The lever model, actually ordained and demanded by the accepted equations, visually and conceptually leads one to a useful model for predicting and cataloging rod behavior.

We have from the above two of the three elements needed to create such a model. We have a standardized force that is line weight specific, and a measurable rod shortening in response to that force, that is, a functional and cast specific exact measure of stiffness. What remains is the variation, rod-to-rod, in that lever length to less than standardized force, or to additional force…that is…a measure of taper within the working flexion range.

In other words:
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