To draw an arc, we can start by drawing a line, so I start drawing somewhere and then I wiggle the pencil and I still maintain contact with the ipad, you see wiggling changes a line into an arc, an arc into a line and forward and backwards. So this is very very easy to do.
So by drawing an arc you define the start and the end point. So let's say one endpoint should be there and with the pencil I select a start point and reposition it there and you see now we also have this point in between on the arc, which we can move around for example to adjust the size of that arc.
Now let's say I would like to create a perfect half-circle.
There are two ways how we could do this: for example I can move this point to the grid. In this way I make use of the grid to create a perfect half-circle.
But let's say we don't have that luxury, so we need to approach it differently. Well we can actually use the nice dimension tools. So for example I just draw another line here. Great!
And then I know that a perfect half-circle is perpendicular to a line, so I can set this one to 90. And then you see the line moves up, so why did this happen?
Well the thing is actually: I have selected the line, so now the line is 100.93 degrees to the arc, but actually I want the arc to be 90 degrees to the lines, so I actually should select the arc and then type in 90 and there you see the left and the right value is all 90. So you see this is very very easy, it's perfect for drafting.
Also here I can draw a line and for example make the line perpendicular to the arc by simply adjusting the angle I can also make it tangent by adjusting the angle.
So this is very powerful.