For example for variance of delta x, some sources have it as (delta*x)^2 with a bar on top, and others show it as <(delta*x)^2>. Are they referring to the same thing?
dont the authors define their notation the first time they use it?
is a notation i've seen for the variance before
is a plausible notation for the estimate of the variance
i've never seen and wouldn't understand if i saw it.
NB i edited the content of this post while OP was typing the reply below
Here are the sources. The first is a youtube video (watch at the beggining he says variance of delta x), and for the second one, go to page 10, equation 2.19