My suggestions would be to first, change the symbol for division to /, which is more distinctive. It's used in math books as well as on keyboards so should be common knowledge. Secondly to add color to the symbol font, to further distinguish them from each other, perhaps with a legend off to the side or bottom (for example: a pink +, a cyan -, a green x, and a yellow /) Enlarging them a bit would help as well, but I'm guessing they are already as large a possible. Though if not, enlarge them please!
Cathie Vishnevsky writes: