This may have been discussed somewhere else, but in a 2 minute search, I couldn't find it.

I am using SW 2018 SP5

OK, I use "Make equal" for lines all the time.  I prefer to use it instead of adding two dimensions and linking one to the other.

However, I just ran into a situation where it confuddled me.  And created something that, if I hadn't caught it, would have cost us some money in rework.

The situation:

I have two lines in 2 different revolve sketches that I want to be equal length.

These two lines are NOT on parallel planes.  The planes are 35 degrees from each other.  I thought that it was impossible to make lines equal length if they were not on parallel planes.  However, when I selected it, I wasn't even thinking about that and it worked!

Here are the two lines:

The length of the line on the right is 0.12475" long (creating a diameter of 0.2495" once revolved).

The line that I matched it to after "Make Equal" has been applied, is 0.1022" long.  Which the projected length of the first line, when you project it onto a plane at 35 degrees. Example:

So, when I asked it to "make equal" it not only let me do it, but then proceeded to make the line the incorrect length and instead made it the projected length.

I am glad that I noticed it.  However, I may not have if the 2 planes were 1 or 2 degrees from each other.

Here is a test:

The 2 planes are 45 degrees to each other.  The 1st line drawn is 2" long.

Drawing a line on the angled plane and making it "equal length", makes the line 1.414" long:

Simply changing the angle of the angled plane to 10 degrees changes the length of the line to 1.97":

In the case that I originally used, it was an easy catch, and now that I know that this happens (it only happens to 2D sketches and NOT 3D sketches), I can prevent it.

However, if I could imagine a scenario in which I have an imported model and I am sketching on 2 different surfaces and they are off by half a degree or so, this could be dangerous.

Things to watch out for in the future.