This was a bit of a new concept for me as I had never really thought about coordinate graphs having ‘handedness’, I just took for granted what I learnt in maths at school, that along the x axis, right is positive and along the y axis, up is. If someone chose to do it the other way they were just being quirky.
We speak of ‘handedness’ because human hands provide a quintessential example of chirality- like Ben says in the lecture, you can’t fit a right glove on a left-hand and vice-versa.