Meh, I don't really feel it's needed.

It is best that you keep a calculator next to you, but perhaps a calculator button which could appear as a tab alongside the inventory tab?

 

It isn't a problem, but a convenience which could have some useful features such as (quoting from the thread which deyan2 posted) a K (1,000), M (1,000,000) or B (1,000,000,000) button? It could also remember certain numbers (A use would be if you are selling rune arrows for, uh, whatever the price is, you could then remember the price in the calculator which is remembered until you log off, and then simply multiply the value by the order amount for each trade).

 

 

 

Great idea! Then you could use it to calculate xp also. Then you wouldn't have to come all the way here to use skill calcs.