Why not allow numeric fields to do arithmetic computation?

Question

Is there some reason to disallow arithmetic operation in numeric and other similar inputs? Or is it just lazyness of implementation. Some examples:

• I can not write an order for 6 bolts for 17 machines in form 6*17. (The form can not know or care that i have actually only 16 machines and want a spare set)
• Drawing application does not allow me to type 10/16*1920 for height
• I can't type 1/3 (*100) in a scale field
• I can't fill in 355 * 1.13 to add a foreign tax in my banking application (because im transfering money to a friend to pay for my share, no the bank can not know why id want 13% on top, no local tax is 13%, also all local costs are tax included anyway.)

...

WTF? Its 2015, you don't seriously expect me to page out to another app just because your default inputs can not calculate the stuff for me. Hell, half of the time you see other people doing this with a pocket calculator every 3 or so inputs.

So there clearly is something fundamental, at play. Because why on earh does not every single gui toolkit implement this for everything?

Its not like I assume the system solves the integrals for me, or even trigonometry. Just the 4 base operators +, -, * and /. Neither do I expect (but would appreciate) unit conversions.

PS: In fact quite many very good apps do this. Adobe does this in the design apps. Google search field does this to name a few you probably know. Im more or less asking why not all apps.

Answer 1

One of the many great things about my much beloved and sadly departed Macromedia Freehand tool was this very feature. You could put any mathematical equation into a field and it would calculate it on the fly for you.

A lot of CAD software will do this. Including Sketchup.

I agree that it's a great little feature. It can be completely unobtrusive as well in that it doesn't need to clutter or add to the UI at all. Just a nice 'aha' that can take place on the back end.

Which, answers the question:

why on earh does not every single gui toolkit implement this for everything?

= Because it's not an aspect of the GUI really. It's a calculation done on the back end. (Yes, it could be done client side on a web page, for instance, but still, it doesn't really affect the UI that the user sees or interacts with)

Why don't all apps do this? Well, not all apps are designed for you. :) It'd be a nice feature in a lot of apps, but like all features, it often comes down to a decision based on time, money, marketing, target audience, prioritization, etc.

Answer 2

It would be easy to do, as evaluating expressions is a solved problem.

However, in most cases it is not what the user would expect and also the validation, error-reporting, etc is a lot more complex, as you'd have to have some way of showing the user if their input wasn't valid.

In general, for a well-designed application, it shouldn't be necessary to do this, as it should capture the data it needs and figure everything else out for you. So, for the tax example, it should know the appropriate tax rate(s) and apply them. If the user supplies them, what if you do a typo and put "355 * 1.12" instead of "355 * 1.13", there'd be no way for the system to know that was wrong.

In summary, it could easily be done (make each field behave like a cell in Excel), but it isn't necessarily desirable.

Answer 3

I don't think it's laziness, I just think people are not convinced it's a user need, somehow. No, I agree it should be a standard. I'm using it all the time in the Illustrator, literally every session. It could come handy pretty much anywhere — in the personal fin tech, in quantified self apps, anywhere there are data inputs.

What would also be nice is calculations in date pickers, something like "May 4 2015 +15 days".