Indeed. Lightroom uses the shift key to snap a mask to 0 and 90 degrees. This really helps.
When shift is not pressed, any angle is possible.
@StevenL , using a modifier key instead of a shaky automatism could be a nice change.
Other than that, we’re way off-topic 
Then it is not possible to shorten it again and keep some angles without a “kind of snapping” (= change of angle du to something like number imprecision somewhere in code (moving by steps instead of continuously)).
Some short gradients at some angles are impossible to acheive.
And indeed precise angles like those are sometime difficult to acheive.
Possibly, better still, a modifier to stop rotation when altering the gradient length?
There of course are several way to acheive this with precision.
3D softwares even allow to do this (move and rotate simultaneously and in 3 dimension, not 2, and interactively) on a projection on a plane of a 3 dimensions space extremely precisely.
DxO way is not the good one.
Move the dashed line instead of the round gizmo to not alter the chosen angle.
Indeed. My bad. I use to use a one step method in other softwares and skip this way (multiple steps) when need to go fast.
Yes it works fine.
Mathematics has never been one of my strong suits, but I suspect he may have been metaphorically referring to a mathematical “moment” in Physics or Statistics rather than a moment in time, which is the more common usage of the word in English.
At any rate, I do now understand his intent. It is nearly impossible to accurately set the angle of a control line when the dashed and solid lines are too close to one another.
Hi Thomas,
as you still seem to cling to words, I went back to where you “jumped in” here.
Masking with a Gradation / Graduated Filter exists since long in Photolab.
→ You can extend the selection with the manual Brush tool resp. subtract with the Eraser.
In PL5 DxO added the Control Line tool, which is based on the Control Points’ functionality, and both got adjustment sliders for Chrominance and Luminance allowing to refine the mask.
→ To extend their selection you can use normal (positve) Control Point and Control Lines, while to subtract you revert them with a modifier key*) as negative CPs and CLs.
→ And of course you can also extend / subtract CLs with CPs (and vice versa).
*) in Windows = ALT // for Mac please check the help overlay in the program
For some demonstrations I recommend to go back to former video tutorials, e.g.
PhotoLab 5 and FilmPack 6! Big upgrades from DxO
(or here for overview)
Powerful New Feature in DxO PhotoLab 5
( or here and here for overview)
Experiment and don’t hesitate to ask further questions. 
Wolfgang
Thank you , Wolfgang, for encouraging me to dig in and stay the course. Masking in PhotoLab requires a mental paradigm shift to alter the way most of us have learned to think about how graphical selections can be created. Using lassos, magic wands, etc. to inadequately mask graphical elements as selections in countless programs for nearly forty years had, I dare say, created a rather pervasive mental roadblock to overcome.
I do appear to be making progress now. Still confused, though, as to the sphere of influence of the Control Line. I had assumed the selection would be limited to the area between the solid and dashed lines, but that’s clearly not the case.
The Control Line masks at 100% everything to the “outside” of the solid line. The section between the two lines is a gradient from 100% to 0% at the dotted line and everything “outside” the dotted line is not masked.
But don’t forget that the pipette decides what tonality and colour the mask is based on and that can be placed anywhere (even outside the mask) where you can find an example of that tonality/colour.
Use the B&W mask to see precisely what is masked. What is white will be affected, what is black will not. The Luma and Chroma sliders are extremely important in helping refine things that are masked grey towards either black or white.
You can regard Control Lines as a two step tool. Start by defining the mask and, only when you are satisfied, hide the masks and make adjustments using the LA palette.
There are instances where it’s easier to observe the effects of a mask by setting the desired setting to an extreme value and setting up the mask based on that. You’ll likely also have images where it’s better to combine multiple control lines and duplicate and invert them… .
Whichever route you choose, when you’re experimenting remember to use virtual copies.
tried to put together an example
→ watch the settings on the RHS as you go through them
all Local Adjustments → OFF
LA Control line → sky
LA Control line → clouds
LA Control line → grass
all Local Adjustments → ON
OK, I’m becoming steadily more competent, at least with images that require only one or two separate control lines that don’t in any way overlap one another.
Experimenting with a recent image, I tried using control lines to separately adjust the sky, the San Francisco bay beneath it, the city of Fremont as seen from 1600 feet above it and finally the foreground consisting of mountain foothills cascading downward toward the city. In addition I used control points to mask one of two of the actual subjects of the image - an old, lone California Oak Tree atop the nearest of the foothills (a setting full moon beside it).
The elements masked with control lines were all more or less vertically independent of one another. The tree, however, masked only with a collection of control points, cut across the city and bay masks and partly into the sky mask.
Somehow, I was unable to shrink the bay control line mask, which lay between two other control line masks, to cover only the bay. A small section of the sky above it remained selected no matter the adjustments of Chroma and Luma or the placement of the pipette.
I don’t know if it is correct to relate to PhotoLab masks as layers, but it appears that overlapping masks in PhotoLab don’t behave in quite the same way as layers do in apps like Photoshop. Can PhotoLab masks be made to intersect with one another in a similar way that layers can be merged or blended in Photoshop?
I’m leaving tomorrow morning to spend the weekend in Mendocino to celebrate my wife’s 80th birthday, so I won’t be able to respond to potential Qs and/or As until next week. Thanks in advance for future insights, advice, etc.
