typefaces - What are the differences between Helvetica and Arial?

I've heard there are a number of slight differences between these two similar fonts, is one better than the other for different contexts?

Answer

As far as the difference goes, you are right. There are some character which are slightly different however the difference goes way beyond just the comparison of the character.

Here is some explanation on ilovetypography

Here is a site which shows you how to spot the difference on awayback Helvetica vs. Arial, and includes amongst other things this helpful chart (which they credit to Ragbag):