Accuracy of the human eyeball and hand

[fizzy]

Bit of an odd thread but then it is late..............

Has anyone built something or measured something - seems pretty spot on when you measure but then when you actually SEE it then it looks wrong? or you get something only a few thou out but it looks was off by eye?

I have noticed this a few times. Surprising just how much we can spot such things.

Also despite all the marvels of modern science it amazes me that the best surface tables are hand scraped. The best telescope mirrors are hand ground.

Funny how humans can be better than machines at some things.

 

[DanielW]

Yeah you put a shelf up and use the spirit level and her indoors says its wonky,and you know she's right when you stand back and have a look.....go figure that one.

 

[s410man]

Yeah you put a shelf up and use the spirit level and her indoors says its wonky,and you know she's right when you stand back and have a look.....go figure that one.

new spirit level?

 

[julianthegypsy]

new spirit level?

Or straighten the walls, wonky walls or floor is the usual cause of that, you look at what's level in relation to other things. If the wall's wrong, the picture has to be wrong too for it to be right!

 

[cumbriasteve]

I built a stone fireplace for a mate when they were all the fashion, when it came to placing the wooden mantle on the last row of bricks the level said it was spot on but when sitting on the sofa it looked like it was sloping.

Rechecked the spirit level and was spot on, tried again and still looked off, ended up ignoring the level and setting by eye, with a 4mm packer at one end and it looked perfect.

Put it down to an optical illusion caused by the wall décor or the bricks.

 

[Rig Pig]

Houses are rarely built with all surfaces square and true to each other, especially old houses, I had hours of fun fitting my new kitchen, shaving bits off the backs of the units to match my drunken walls, tiling is going to be fun!

 

[CompoSimmonite]

I've noticed now I've got varifocal glasses things don't seem as straight despite know they are.

 

[ajlelectronics]

I have astigmatism. Imagine how much fun that is? The shape of an item can vary depending on how my glasses are sitting on my nose.

 

[CRB]

Or straighten the walls, wonky walls or floor is the usual cause of that, you look at what's level in relation to other things. If the wall's wrong, the picture has to be wrong too for it to be right!

Too right.

Trying to educate people that you need a level, not flat, datum for a spirit level is like knocking a hollow bone near-sphere against a not-vertical-or-flat-in-any-direction-brick-built-plastered-surface.

 

[Kayos]

I fitted central heating for many years, and after a few years everything was done by eye as I got bored of telling customers my work was right and the house was bent

 

[brightspark]

Yeah you put a shelf up and use the spirit level and her indoors says its wonky,and you know she's right when you stand back and have a look.....go figure that one.

if u look at it head on it will look and be accurate providing the floor and ceiling are level if there not it gives the elusion the shelf is not straight, put 2 switches on a wall 8 foot apart and level look head on and there right . stand at an angle in the corner of the room and look and the furthest away looks higher

 

[brightspark]

I fitted central heating for many years, and after a few years everything was done by eye as I got bored of telling customers my work was right and the house was bent

thats where practice comes in sometimes u have to make a compromise and split the diffrence between being level and the bent wall

 

[julianthegypsy]

I have astigmatism. Imagine how much fun that is? The shape of an item can vary depending on how my glasses are sitting on my nose.

I have exactly the same problem! Trying to line things up before I weld them is a nightmare, I look at things and they are off at odd angles, then I lean my head and they go off the other way, then I have to stand back and adjust my glasses and tilt my head both ways to be sure. If I ever lose my sense of balance as well there will be some decidely wonky stoves coming out of my workshop!

 

[brightspark]

I have exactly the same problem! Trying to line things up before I weld them is a nightmare, I look at things and they are off at odd angles, then I lean my head and they go off the other way, then I have to stand back and adjust my glasses and tilt my head both ways to be sure. If I ever lose my sense of balance as well there will be some decidely wonky stoves coming out of my workshop!

join the club its called use a square strait edge and spirt level if u cant do it by sight

 

[pedrobedro]

Use your level and draw a line then turn the level round and draw the line again and adjust the bubble if it is adjustable. Our house is neither square nor level so it's a pig to put anything up and have it look right so everything is eyeballed as well as spirit levelled. I ask the wife if it looks right before final fixing that way I am covered

 

[Kent]

Just been converting a Weekly hire Canal Barge to a day trip boat. Towards the end of the job now, I started off with angle finders, levels of all manner etc. Ended up with a tape measure, bit of string and rack of the eye. To be fair measuring equipment has its limitations look at an actioner use lamp blacking in the guntrade for example.
Optical illusions are very real however to I tend to check and re-check both ways if it really matters, sitting square and level often depends on your datums. For instance I have trued the window grills to the centre mullion on the workshop windows (which I trued with a level on fitting) - unfortunately the stone buttress between two of them and the slightly out of true lintels make them look droopy (hope to correct that next summer when I render it)

 

[julianthegypsy]

join the club its called use a square strait edge and spirt level if u cant do it by sight

I have about half a dozen squares! It's when I look at things and can't figure out if they're parallel that it gets interesting...

 

[MattF]

I tend to trust eye over level etc. on most things these days. No point something being perfectly level if it's either going to look like crap else not mate up properly. Perfection is nice, but good function and fit are far more important. Same with measuring. Spot on is good, but not necessarily always best, and there have been the odd occasions where my eye has caught a small error I've made in measuring too.

I suppose it's like silly little things which you do frequently without thinking. For example, how many can sort through a pile of mixed size screws and come out with a handful of the ones they're after, without having a reference screw or measure to check against? The brain is a weird thing. Some can, some can't, whatever the task.

The reason humans will always pip robots/machines is that we can adapt readily to circumstance. It's an inbuilt ability, whereas machines have to be programmed to have some semblance of that ability, and even that it's severely lacking in scope.

 

[Gritineye]

I once erected a tall advertising tower way out of plumb because the brickwork on the buildings behind had been laid to the slope of the ground, only giveaway was on misty days the water dripping off the top landed 18" to one side of the base!

 

[wookie]

I've built a log shed on my drive that has a good slope on it (30degs), Initially I set the uprights bang-on plumb and it looked awful, it looked like it was falling over up the slope, so I set them by eye and it looks right although I know it's a mile off plumb.