topic Re: Any idea why this equation is not working? in Inventor Forum

Any idea why this equation is not working?

chris — Fri, 03 May 2024 01:51:16 GMT

I do this 100's of times a day, but for some reason, this is not working, an "inch" number divided by an "inch" number?

Yeah, this is going to be a problem!

Re: Any idea why this equation is not working?

SBix26 — Fri, 03 May 2024 01:49:25 GMT

Because Test3 units are also inches. Inches divided by inches should be unitless.

Sam B

Inventor Pro 2025 | Windows 11 Home 23H2

Re: Any idea why this equation is not working?

chris — Fri, 03 May 2024 02:11:23 GMT

@SBix26 Now you have me going back and looking at older parts parameter equations... this can't be the first time I've encountered dividing/multiplying to "inch" numbers together...

well this worked, pain the *** to have to do this, makes the equations so long for more involved equations.

Test3 = Test1 / ((Test2)/1in)

Interesting, iLogic returns the correct number, even though Test3 is inches, and it's written like this:

Test3 = Test1 / Test2

Re: Any idea why this equation is not working?

SBix26 — Fri, 03 May 2024 02:27:02 GMT

It's not logical to expect inches as the result, though. Length divided by length gives you a result that tells you how many times (unitless) the one goes into the other. Can you explain the rationale for dividing length units and expecting a length unit as the result?

Sam B

Inventor Pro 2025 | Windows 11 Home 23H2

Re: Any idea why this equation is not working?

chris — Fri, 03 May 2024 02:48:45 GMT

actually, I wasn't thinking about the unit, I was just thinking about the number, because this isn't an issue with (addition and subtraction), no big deal, I've made the change now, but something like this is a lot easier to write than the highlighted equation (see image)

Re: Any idea why this equation is not working?

cidhelp — Fri, 03 May 2024 07:15:42 GMT

Hello @chris ,

if the parameters have a length unit, I can type like your red annotation. On pressing Enter Inventor is adding some units (grd is german for deg and oE for ul) but results correct.

(view in My Videos)

Re: Any idea why this equation is not working?

CCarreiras — Fri, 03 May 2024 10:02:47 GMT

Other option is to quick change the expected unit:

Re: Any idea why this equation is not working?

SBix26 — Fri, 03 May 2024 20:31:08 GMT

If AS2 is a length (inches), then your equation as you show in red makes perfect sense. However, you have AS2 in degrees, so I'm not at all clear how that works.

If AS2 is inches, then the equation is this: LOD * sin (45 deg / 2 ul).

Sounds as if you have not had to deal with calculations involving measurement units very much. Units are a great way to check that you've gotten an equation formulated properly. If you are looking for area, for example, and your equation doesn't end up with square length units (in^2, for example), something is probably not right with your equation. If you're looking for speed, your equation needs to divide distance by time (m/sec, for example).

There are the odd situations where the units don't make logical sense (though I can't think of one at the moment), and then you have to do as you've shown in your image. But that should be extremely rare in any real-world application.

Sam B

Inventor Pro 2025 | Windows 11 Home 23H2