Arc inconsistent behaviour

Call the LINE command, click to start. Enter a distance eg 500. The virtual line appears, 500 units long, and stays that long regardless of where you move the pointer to finally click to place it. (or you can just press enter at anytime to set the endpoint direction), but the length is always 500 units.

The point is that the length can’t be overridden by clicking.

The same applies to drawing a 2 POINT CIRCLE, or an ELLIPSE BY CENTER ie the radius or diameter can’t be overridden if it has been set numerically.

However, if a 2 Point Arc is drawn, the same does not apply. If you click anywhere within the area defined by the numerically specified arc, ie less than the radius, the click will overwrite the unit setting and the arc radius will be defined by the click relative to the starting point.

Basically, if you go to the trouble of setting the numerical constraint, you obviously want that to be active throughout the command, and allowing a random click to override it means you end up with inaccurate results…

I see this has been the case since at least V5, but it’s causing me a little bit of grief, since I expect it to behave as its cousins above, and I would therefore request that this behavior be altered to follow the same rules as similar commands.


Hi @rabbit

Regarding Arc 2Pt.

What I see here is that if ie. the input is set to 50, indeed, the value can be overridden with a mouse Klik.
When the input is set to 50mm then, the numeric value is kept and cannot be overridden.

Tested on Rhino for Mac
Version 7 (7.5.21096.11002, 2021-04-06)

Rodolfo Santos

Ha - maybe that’s a mac thing?
My units are set to mm all the time; it makes no difference if I just enter the number or add mm after the number, still the same result.


Yes, I told that my contribution may help others to figure out if this is a generic issue/behaviour or a specific one…

Rodolfo Santos.

i have seen some bugs being fixed in recent version regarding lengths of commands for the windows version, not sure anymore if arcs where part of it since i am also running mac and dont follow that so exact. anyway do you run a recent update?

Yep, these are all downloaded today…

Hi rabbit - the distance constraints should all work in the current service release -SR5 - there was a bug in 7.4 initially, and that was replaced by a 7.4 ‘hot fix’ to correct that problem and one or two others … So, can you verify what exact version you are running?


V7 SR 5

(7.5.21100.3001, 2021-04-10)


(8.0.21103.8305, 2021-04-13)

Thanks Pascal

Yep, sorry, I see that now in Arc > StartPoint.

RH-63830 Arc > StartPoint distance constraint.