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Is this a legacy thing or does a tilted cursor serves a purpose? I can tell that, the angle provides a totally vertical left edge which helps when highlighting text but what else apart from that?

EDIT: When cursor is swapped by the little hand cursor when hovered over buttons, the angle seems to be smaller. Why the difference?

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Modern times. For generations, kids used to ask the same thing about bananas. –  Max Feb 17 at 14:57
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When you're highlighting text, the cursor changes to an I-beam on any decent UI. –  Kaz Feb 18 at 6:46
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I have seen straight cursor in some old DOS GUI apps and have also tried it in Windows and Linux - straight cursor just looks and feels nasty like handling a spoon straightly perpendicular to your face when eating (feeding yourself) or positioning your elbow to the center of your body when giving a handshake... Also can cause some Freudian associations when thought about :-) –  Ivan Feb 19 at 4:26
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Also, consider that some text (for cultural reasons or others) are written vertically, having a straight mouse would hide the next letter after the one you point at. Making it go towards the right side and down makes it very practical in many situations. –  Aki Feb 20 at 10:30
    
The historical reasons are given by some great answers here. However, I would like to add that a tilted pointer hides as less information as possible. Of course not in all cases, but generally, data is aligned vertically or horizontally. Therefore, the diagonally aligned cursor is not in the way. –  danijar Mar 1 at 1:45

7 Answers 7

up vote 568 down vote accepted

This is the historical reason:

Concept drawing of the standard mouse cursor at an angle

(Concept drawing taken from document: VLSI-81-1_The_Optical_Mouse.pdf)

The mouse, and therefore the mouse cursor, was invented by Douglas Engelbart, and was initially an arrow pointing up.

When the XEROX PARC machine was built, the cursor changed into a tilted arrow. It was found that, given the low resolution of the screens in those days, drawing a straight line (left edge of arrow) and a line at a 45 degree angle (right edge of arrow) was easier to do and more recognizable than the straight cursor.

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And of course Bill copied it from Steve who copied it from Douglas ;) –  Bart Gijssens Feb 17 at 13:38
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@jjt the right edge of the arrow is 45˚. –  Jakob Weisblat Feb 17 at 17:20
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So pixel layout is the real reason :) To make it vertical and still look smooth the cursor would have to be twice as wide. Also that most def. is 45º, just think about the image... it's a grid.. one line goes down down down down, the other line goes down right down right down right. It must be 45º –  Albert Renshaw Feb 17 at 17:41
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@AlbertRenshaw: ...at least if you assume square pixels--but that wasn't a given in those days (e.g., it wasn't normally true of an EGA or Hercules card at their maximum resolution). –  Jerry Coffin Feb 17 at 20:55
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Your answer got on Gizmodo :) –  Ciprian Pălici Feb 17 at 21:48

Take your right hand and point to your question.

There, you see.

finger pointing at screen

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This post does not cite any references or sources. Please help improve this post by adding citations to reliable sources. Unsourced material may be challenged and removed.

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What if I'm left-handed? –  Erik Peterson Feb 17 at 18:49
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Ok, that's your hypothesis. Can you give evidence that this is actually the reason, or even had any basis behind the 2D, small, on-screen arrow? Surely if this was the case then it wouldn't be an arrow at all, it'd be a finger? –  JonW Feb 17 at 18:58
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Clearly no one is left handed ;-) –  Akrikos Feb 17 at 18:58
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The average you is not left handed. :( –  Júlio Turolla Ribeiro Feb 17 at 19:57
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I actually like this answer the best. I understand the technical answers and I viewed Doug Engelbart's demo where the pointer is indeed vertical. However, this mimics the hand better, looks more natural -- and in addition, it does not obscure the pixels right below the target, which the user is presumably more likely to want to see than pixels to the southeast of the target, when viewing it, due to the heuristic that many graphics employ horizontal and vertical guides. Also, why does it have to cite sources, when it has a picture of a hand? –  Gregory Magarshak Feb 17 at 21:24

In addition to Bart's answer, I'd like to add one more reason.

The reason the arrow was tilted to the left was so that the click position was easier to calculate, because the origin of the cursor's bitmap was in the upper left. This saved the mouse tracking subroutine a calculation on every click (its not much but it helped on older machines).

Source

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@PatomaS: That was a later generalization when machines became fast enough. –  MSalters Feb 17 at 15:13
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While this certainly sounds plausible, your source is just a Reddit post that has no citations in it, so could just be totally made-up. –  JonW Feb 17 at 15:33
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Although this is a theoretical benefit, I highly doubt it seriously informed the decision. Even by the standards of the 1970s, adding two offset numbers is an extremely trivial operation that could easily fit within the mouse update interval. Remember, just like today, there were other pointers in use depending on the application (e.g. text selection, row selection, paintbrush) and they didn't all have (0, 0) origins but worked just fine nonetheless. –  nmclean Feb 17 at 17:05
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@nmclean is right, this answer is completely incorrect. The cited Reddit post is merely a direct copy of this Yahoo! Answers post from 2009, and that post also had no citations. On the contrary, here are two examples of Alto cursors that do not have the hotspot at (0,0): a cross in a circle and a right-pointing arrow. –  Michael Geary Feb 17 at 18:45
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With regard to the calculation time, my ballpark estimate is that it the custom hotspot took between 4 and 8 instructions at 400,000 instructions per second, or between 1/50,000 and 1/100,000 second for each mouse update: news.ycombinator.com/item?id=7253841 –  Michael Geary Feb 17 at 21:35

Low level visual cognition

In addition to the various answers given, there is also sense in a tilted mouse pointer if one considers the visual processes in our brain.

Visual information arriving from our eyes is first processed in the primary visual cortex by the V1 area, then by the V2 area. These two areas recognise low-level visual features (hue, lightness, size, orientation, etc.).

The popout effect

As visual information is processed by these areas, some visual irregularities truly pop out (ie, they are highly distinguishable), which greatly helps visual search (trying to find an item in a visually busy field). The popular name for this phenomenon is the popout effect.

A famous research from 1988 - A. Treisman, and S. Gormican: Feature analysis in early vision: Evidence from search asymmetries summarises many of these popout effects, and the irregularities they involve.

Orientation

One such irregularity is orientation, and it is neatly explained by the following illustration:

3 images showing many vertical lines and how a tilted line pops out

You should find it next to impossible to find the search target in 1 (a straight line in a group of straight lines). But rather easy in 2 - finding a tilted line in a group of straight lines. In 3 it should be equally next to impossible to find the tilted line in a group of tilted lines (of the same angle).

Since vertical and horizontal orientations are the most common ones on screens (and in life in general) a tilted mouse pointer will be more easily found.

More information can be found in Chapter 2 (What we can easily see) of Visual Thinking for Design, Ware 2008.

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I have a feeling that this answer is totally unrelated to the real reason for the tilt, but it is cool nonetheless. However, whenever I need to find my mouse, I just wave it about wildly until I see it moving. –  naught101 Feb 20 at 1:23
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@naught101: I do that too. We should have animated (spinning?) mouse pointers so they really stand out and we don't need to wave the mouse about to see where the pointer is :-) –  Brendan Feb 20 at 8:30
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MIT Lisp Machines had a cool feature to help find the mouse cursor: if you moved the mouse back and forth quickly, the cursor would magnify (the documentation described it as "big like Godzilla"). –  Barmar Feb 20 at 23:45
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@cr0ybot you can already do something like that in Windows. I had a synaptics driver and it had an option to show circles around pointer when certain key was pressed. I don't have that PC right now but may be googling might help. –  user13107 Feb 21 at 3:19
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@user13107 I'm sure that's actually a standard feature. Control Panel|Mouse|Pointer Options|Show location of pointer when I press the CTRL key. Another option that helps find the mouse (though imho it's less effective and more annoying than the former): Display pointer trails. –  Craig Young Feb 21 at 8:36

In case anyone wonders : some less known interfaces did use a straight arrow as pointed in Reddit

enter image description here

enter image description here

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So strange, I wouldn't even think that the cursor could move. –  jinawee Feb 20 at 17:09
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feels like the computer is flipping me the bird –  Cory Silva Feb 21 at 6:17

I've always thought that the arrow cursor is shaped similarly to your hand if you were point (naturally) at the screen with your (as typically dominant) right hand.

I have no support of this other than my own subjective experience but it strikes me as a natural shape when trying to relate real world interaction into a low resolution computer screen where rendering something resembling a hand would be impossible.

[Edit: Someone stole the only thunder I've ever had on StackAnything. Thanks!]

Hand pointing at screen

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This post does not cite any references or sources. Please help improve this post by adding citations to reliable sources. Unsourced material may be challenged and removed.

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I think this is an actual "non-historical" answer. Otherwise we would've seen reverse-angle and straight cursors in abundance. –  Den Feb 17 at 17:17
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@Den We have not seen user interface operating systems themselves in abundance. Most of the world is based on several operating system hegemonies. –  Kaz Feb 18 at 6:44
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@Kaz - most of games have custom cursors. Old Dungeon Keeper is a perfect example - it's literally a hand shaped cursor pointing the way your hand would - inclined to the left. I am sorry but this answer is the only correct one. –  Den Feb 18 at 11:46
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It's curious how this answer got 2 upvotes but a same answer with an image got 122. –  jinawee Feb 20 at 15:12
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@jinawee: Because people like pictures and don't read words as much. And the one with the hand has an arrogant 'there, I proved it' attitude - despite neither that one or this one being based on any actual evidence, just reverse-engineered guesswork. –  JonW Feb 20 at 17:06

Also, there is another answer to this question. As a rule, the arrow mouse cursor must have one sharp tip (vertex) - because it is an arrow :)

On the other hand, it is better for a mouse cursor to look good and slick.

But drawing sharp tip on a rectangular pixel based display is very hard, especially without anti-aliasing.

The 0 degrees (horizontal or vertical) and 45 degrees lines are the only possible lines that look smooth without anti-aliasing.

That is why almost all arrow mouse cursors are based on one straight and one 45 degrees lines. As a result, the bisector line has angle of 45/2 = 22.5 degrees.

The tail of the arrow is much harder to be drawn well, but it is not so important as well.

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An arrow with edges that are vertical and horizontal, or that are +/- 45 degrees, would also clearly identify a point without aliasing issues, but would obscure more of the screen underneath. Having one edge vertical and one 45 degrees reduces the obscured width. –  supercat Feb 17 at 20:15
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@supercat - Yes. And also, such arrow will have angle of 90 degrees and will look too "pointless" and as a result ugly. 90 degrees arrows are OK for some tasks, but not for mouse pointers (IMO). –  johnfound Feb 17 at 21:23
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Drawing a sharp anything is difficult with antialiasing. If you want sharp, you game the aliasing. :) –  Kaz Feb 18 at 6:43
    
@Arne - It must be 22.5 in order to be OK. But is usually drawn as 2px:1px ratio. That is why it looks a little bit wrong angled. –  johnfound Feb 23 at 22:39

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