Todays post is on measurement technique and theory.
Those of you who are carpenters and scientists will already know this.
But there may be other who don't and can benefit.
(my undergrad degree was in Chemistry- which uses a lot of very precise instruments. That's where I learned this.).
Peteski needs to size the drawings as accurately as possible.
But he needs some accurate reference points.
He does not have the model, so I have to measure it for him.
He needs the nose width so he can perfect the nose herald. Corel Draw can measure lines to the third decimal point (at least). So accuracy can be helpful to him.
At first glance, I could tell him that the nose is 15 mm wide.
But that is NOT the case. It is not 15.000 mm (more on decimals in a minute).
Reason: The line on the ruler has width!
So the technique for those trained in this is to arbitrarily decide WHERE on the mark you are referencing.
The most common options are: Left side of the mark, dead in the middle of the mark, or right side of the mark.
In this case, I'm pretty lined up with the LEFT side of the mark.
So wherever my terminal measurement is, it needs to be to the LEFT side of that mark (whatever it is).
So lets zoom in a little.
You can clearly see that the model extends PAST the left side of the mark.
Now comes measurement error.
From this spot, the only thing I KNOW is that it is more than 15 mm.
From here, I can estimate the next unit (which in this case is the first decimal place).
If it looks like it is more than .1 but less than .2, I CANNOT say that it is 1.5. Because .1 and .2 are estimations themselves, I can never be more accurate than the estimation.
(besides, there will be a SLIGHT error on the other end- exactly how close was I to the left side of the mark when I started).
This is called measurement error theory.
So when I look at this photo (better than with my naked eye, but I might say this if measuring with an optivisor)....
that width looks like 15.2 mm to me. But I could be off at the starting measure by .1 mm as well.
So, the error is +/- .2 mm. So it could be 15.0, 15.1, 15.2, 15.3, or 15.4 mm.
But actually, I can do even better digitally (and check how good my estimation was).
First, when I zoom in VERY close on the starting measure, I was actually pretty close to the mark.
I then import that last photo into CorelDraw. I then draw one yellow rectangle. I then reproduce it exactly. Now I have two. I do that until I have 10 rectangles EXACTLY alike. See below.
I then group those rectangles (one tenths) and size them to go from a LEFT side of a mark to the next LEFT side of a mark. I now have new hash marks for my ruler.
And now you can see that 15.2 was pretty close.
Depending on how accurate I was on the left side of the model, this could be 15.25 mm. Error would be .01 on the initial measure and .01 on this measure so = +/- .02. So the most precise I can be is 15.25 mm (+/- .02 mm).
So the point of this exercise was not to show how many decimal points of a millimeter I can go LOL.
It was simply to show you that in the very first photo above-- that is NOT 15 mm. A novice might have said that. It is clearly MORE- but not much more.
So I'll tell Peteski to use 15.25 as his reference. And he can reproduce that number in Corel Draw.
