I'm planning to use a menu that hides on scroll down and shows up when scrolling up. I know sites that do this that are very sensitive to the scroll up motion and show up at the slightest scroll, which is frustrating, as it results in the menu covering content at a slight scroll up and requires effort to hide it again. I like how Medium's scroll up bar behaves, though.
Are there any guidelines on how the scroll up bar should behave? How much scrolling up should show it and how much should keep it hidden? Should the scroll speed be taken into account and, if so, how?