Back in the day when I was a student at mathscamp, one thing that I was taught and have taken on board since is the advice to always cross one’s zeds when handwriting mathematics, to ensure that they are distinguishable from the numeral 2. I continue to favour this practice and try to promote it myself to any students that I teach, for I find it really makes a difference (and this is probably also the reason why I started to get into the habit of crossing one’s 7s).
Being in the USA, I get a lot of mispronounciation of zed as zee, and I would like to argue that it is an inferior pronunciation for a similar reason. If one enunciates zee, then (this varies with the person, their accent and the context) it can require some thought and/or guesswork to eludicate the difference between 
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