In line with David Fell's comment on logarithmic derivatives, I'd like to
stress that these derivatives are invariant to the choice of units. When we
write x = value times unit, we have, due to the rules of computation with
logarithms:
d log x = d log value plus d log unit.
d means in fact a difference, so d log unit is:
log unit - log unit = 0. So the unit does not matter.
I hope I have not increased the confusion.
Greetings
Stefan Schuster (Berlin)
