About the same time, it seems, as I asked <a href="http://mathoverflow.net/questions/43792/riemann-stieltjes-derivative">this question</a>, a new post appeared on the wikipedia discussion page for <a href="http://en.wikipedia.org/wiki/Time_scale_calculus">Time scale calculus</a> which suggests the Time scale derivative (aka Hilger derivative aka delta-derivative) is the same as the <a href="http://en.wikipedia.org/wiki/Radon-Nikodym_derivative">Radon-Nikodym derivative</a> of the <a href="http://en.wikipedia.org/wiki/Lebesgue%E2%80%93Stieltjes_integration">Lebesgue–Stieltjes integral</a>. Do you agree that the time scale delta-derivative is a Lebesgue–Stieltjes derivative with the appropriate weight function? (The notion of Lebesgue–Stieltjes derivative being similarly defined to the Riemann-Stieltjes derivative of my previous question.)