I was speaking with a friend of mine earlier and he said "Oh look, delta, the sign of uncertainty" (he doesn't study physics often so had only seen in in Heisenberg's Uncertainty Principle equations). I said "Actually, delta is used to express change in variable or quantity, and is only used for uncertainty in Heisenberg's Uncertainty Principle and other such equations".
When I said "other such equations" I meant the ones that are identical to the most famous Uncertainty Principle equation, which just a change in variable, for example: you can't know both the direction of a rotating object and how fast it's spinning, as well as there being uncertainty in the relationship between the number of photons in a light beam and the phase wave associated with the beam (both are expressed with a similar equation to Heisenberg's Uncertainty Principle and use the delta symbol to represent uncertainty.
Was I wrong? Are there other reasonably well-known equations that use the delta symbol to express a variable that isn't change in variable/quantity or uncertainty?