You could expect an error about 4 minutes for your latitude and more for your longitude. If the steps in your table are bigger it´s about half the step (17 minutes in the example of the post) if you don´t interpolate. Because the rate of growth for the shadow is zero at noon your error in getting the shortest length will be minor but you´ll have a hard time to get the time.<br>So for the original example (stranding somewhere or making a forced landing) it may be of some help. For a hiker it´s of limited use. Provided the hiker keeps track of his movement, he will know his position at least as accurately. So I´m not too surprised that some people would rather practice firemaking than this navigation method.