TD:LR - Only the equations and bold question at the bottom are part of the puzzle; the rest is just flufftext.
After a long time of searching for the origin of the device I previously posted about, I have finally managed to track down it's creator. The device comes from a small shop out in a sleepy village in the middle of nowhere. It seems the owner is an odd sort who creates seemingly pointless devices of this ilk and then sells them to make a living. Well, obviously I couldn't resist a visit to this place myself!
Having arrived and entered the shop - a relatively small place considering all the space avalible in the village, and every shelf overflowing with contraptions & curios - I wandered over to the first thing that caught my eye. It was another calculator-ish thing, much like the last.
At this point I first noticed the shopkeeper - a short, old fellow who might be confused with a goblin if such creatures actually existed. The desk was so tall and he so short that I had not previously noticed him peering over the countertop toward me. Feeling a little anxious in his gaze, I decided to distract myself by plugging equations into the machine I had just picked up.
$4 + 5 = 9$
So far, so ordinary.
$37 + 81 = 1$
Or not. Hmmm. Well, let's try something more complex.
$256 + 72 + 25 = 2$
Most odd. Unlike the previous device, this one has all four main operators. Lets try a different tack then.
$103 * 63 = 9$
Oh, and brackets...
$(413/31) + 12 = 5$
I still don't get it. How about this?
$893 - 265 = -2$
Well, this all makes no logical sense. How is 893 smaller then 265? Uh, okay, maybe if...
At this point the 'goblin', who had somehow managed to sneak up upon me from behind, leapt up and grabbed the device from out of my hand. "You use it, you pay for it." he said, grinning and pointing toward a price tag on the shelf I had not previously noticed. "£499! For a calculator that doesn't calculate!" I stammered. "Well," said he, "I guess you don't need it if you already know what it does. How about it then?" He spun the device around in his hand. "If you can tell me what my genius invention does, you may take it for free; else you'll pay what I'm owed."
Well, I certainly wasn't about to spend £499 on a device this useless. I stood for a while in contemplation, before answering and leaving with my souvenir - without handing over any money, of course.
I now pose to you the same question. What does this device do to calculate it's output? What would be the result of the calculation $123 + 456 - 789$?