Curve length dimension not giving correct length


#1

Hi,
V5
Draw a circle Rad 100mm.
circumf is 2 x pye x R

thats 2 x 22/7 x 100 = 628.5714

slice circle in half, circumf is now this / 2 = 314.2857

Curve Length dim gives 314.16

lets try a 500mm rad circle cut in half, should be 1571.428 per the maths but Curve length command gives 1570.8

why ?

Steve


#2

Are you sure your maths is correct? 2 pi 100 = 628.3185 according to my calculator, not 628.5714.


#3

Yeah I’ve never heard of using 22/7 as a shortcut for Pi.


#4

22/7 is not pi… Pi cannot be resolved by a mere fraction…


#5

Me neither and it doesn’t equal pi, its a bit out.


#6

Hi

We learn something every day, we were told at School pi was 22/7 and that has stuck in my head through all the yrs since, I have been using that as pi !

damn !

I shall instead remember the number 355/113 as a better approx. My calculator hasnt pi on it.

Steve


#7

If you type in your values into a calculator (even your iphone calculator) you will find that Rhino is correct. As Mitch and others pointed out 22/7 is just an approximation.

Dan


#8

Nope. Pi is 3.14159265…


#9

Buy a new calculator. Or get a free app for your phone!

You can probably buy a calculator with pi for about the price of lunch.

Dan


#10

Your computer has a calculator that has pi on it. Go into the view menu and choose scientific. I’m pretty sure it was already there in XP…

–Mitch


#11

…and maybe you can even have a slice of pi for dessert after your lunch… :smile:

–Mitch


#12

I shall treat myself to a scientific calculator when I get a chance.

Steve


(Pascal Golay) #13

As mentioned, it’s in Windows already. No treat needed.

-Pascal


#14

I prefer though a calculator on my desk, doesnt obscure my screen or vanish under another window :slight_smile:

Steve


(Willem Derks) #15

Hi Steve.

FWIW:
Rhino has 2 build in calculators as well, I’m on my phone now but if you type “calc” in the command line I guess autocomplete will suggest their commands.

Willem


#16

I had figured what the problem was as soon as I saw the comment about 22/7. I remember that from… Algebra? but they also pointed out that it’s an estimation only accurate out to 2 decimal places.

Or even better yet, since your calculator doesn’t have pi, use the built-in Windows calculator. When you first run it, it’s just a standard calculator. But go to View, and Scientific and you’ll get your pi button as well as all those other functions (sin, cos, tan, etc).


#17

Hi,
trouble with the windows calc is the times function asterisk is like a full stop, stupidly minute. also it either gets in the way on screen or disappears and I prefer to use fingers on buttons. lot quicker.

good to copy result to clipboard though.

Steve


#18

The windows calc works fine using your numeric keypad (assuming NumLock on), no need to click on anything… What I always do…

–Mitch