Hi.

I'm pretty new using Inkscape, so I'm in the learning period now.

I use to set Inkscape measurements to mm instead of px. That is - everytime I start on a new project, I change Default units, Custom size/units and Grid units into mm.
I haven't found out (decided) if this is right or wrong, but I ran into a little problem.
When I move an object using Shift + arrow button, the step lenght is totally unpredictable. Is there any settings to get Inkscape to move an object by custom step length?

And is there any way to get Inkscape use mm as default units everytime it starts up from scratch? I was thinking if I could just solve this by making a template and have it on the desktop. But then I need Inkscape to open a document as template so I don't run the risk of overwriting the file accidentally by hitting Save instead of Save as.

the file default.svg is what determines the units in every new document . setup your doc the way you want it and then save it as default.svg replacing a file in the same location as the current one (do a search - on windows it should be in the inkscape/share/templates folder) save a copy of the original so you can easily return to factory setings

the arrow keys are very precise but take a little practice. plain arrows use the current magnification to move a fixed number of pxels. this is settable in prefs. alt arrow moves a fixed amount no matter what zoom you are at.

When I move an object using Shift + arrow button, the step lenght is totally unpredictable. Is there any settings to get Inkscape to move an object by custom step length?

I found this in the Help menu > Inkscape Manual (the tavmjong bah Guide):

"•Arrow: Move selection by the Nudge factor (2 SVG pixels by default).

•Shift+Arrow: Move selection by ten times the Nudge factor.

•Alt+Arrow: Move selection one Screen pixel.

•Alt+Shift+Arrow: Move selection ten Screen pixels."
(this page)

So it seems that even though you are using mm, the arrows still move things by pixels. In Inkscape Preferences > Steps, you can change the number of pixels, but it appears that the units must be pixels.

(That doesn't seem rational to me -- it seems that everything should use whatever the user has set for the default. It also seems to me that the default measurement should be set in Inkscape Preferences, while still having a setting in Document Properties for the individual documents. I guess I don't depend on the arrow keys for precision, in my own work, or else I probably would have submitted this issue as a wish list "bug" report.)

I think there may be a distinction here worth noting, and that is the difference between an "SVG pixel" and a "screen pixel". I don't know what that difference is, but I'm thinking it was written this way on purpose, which should mean there IS a difference. It's my understanding that an SVG pixel is based on a screen pixel, but again, I don't remember specifically what the SVG pixel is. It may have something to do with the zoom level.

Anyway, what I'm trying to suggest, admitedly while getting a few other questions answered, is that maybe using [Alt+ arrow]and [Shift+ Alt+ Arrow] would work better for you.

Unless you are saying that it sometimes moves the object/node by 10x, and other times by 15x, or 4x, or etc.? If that's what you're saying, then I'm afraid I don't know what could be causing that. ....unless the SVG pixel indeed has something to do with the zoom level. That would mean that at different zooms, the arrow keys would move things by different distances.

And is there any way to get Inkscape use mm as default units everytime it starts up from scratch?

I don't think so, but I think there should be!

But then I need Inkscape to open a document as template so I don't run the risk of overwriting the file accidentally by hitting Save instead of Save as.

There IS a way to do this, but I don't know what it is. Hopefully someone else can cover it for you. Oops, I see druban posted the answer to this while I was typing. But I'll post mine anyway, because of the Step info I've provided.

All best