# Curve length dimension not giving correct length

Hi,
V5
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

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

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

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

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

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

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

Nope. Pi is 3.14159265…

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

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

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

–Mitch

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

Steve

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

-Pascal

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

Steve

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

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).

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

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

–Mitch