My Calculus text describes positive curl as counterclockwise by convention. I found this nice animation of curl:
Here: https://instruct.math.lsa.umich.edu/lecturedemos/ma215/docs/16_5/examples.html
(Stack exchange appears to have erased that the picture is animated, see original site to observe the rotation)
The site describes curl as satisfying a right hand relation.
However I noticed the coordinate system in the illustration is left handed — if I point my left thumb along the positive x-axis my fingers curl from +x to +y — as I understand it the defining feature of a left handed system. Similarly if I point my left thumb in the direction of any of the upwards green curl vectors, it seems to follow the rotation at the given paddle wheel. This would also mean positive rotation is clockwise the opposite of what my text says is the convention.
Do the illustration and the description just not match or am I missing something?