So, after the shoulder we move down the leg. The shoulder and leg move in relation to each other, always, so the measurements we get here can alter measurements we found higher up too. I didn't bother drawing lines on my horse for this - I find the dots easier to measure
We want a longish forearm, I like it to be close in length to the humorous or longer. Forearm helps the horse reach forward and "swing" for each stride. The longer the forearm, usually, the smoother the horse.
We want a shorter cannon - no more than 75% of the forearm, 50% is better. The cannon should be short, with ample bone (I think it's 7" for every 1000lbs) to ensure strength to hold the horse up and stand up to wear and tear.
We want a Pastern which is no more than 50% of the cannon length. Pasterns too long will be weak and prone to soundness problems, and pasterns too short (no less than 30% of the cannon) will create soundness problems as well as a rougher ride. I'm less concerned about pastern slope than I am length... primarily because if you change the slope of the hoof the pastern slope is also going to change - often horses with a poor angle to their pastern are really showing a poor trim or shoeing job rather than any real conformational issue.
Straightness is also being taken into consideration, we want the horse's knee to be flat, and we want a nice straight cannon. The leg is going to be part of what determines the overall long term soundness of our horse. We want to make sure there's enough "bone" to suit the mass of the horse as well.
And lets take a look at foot size, while we're here too. We want to see a hoof which is balanced for the horse's body, the bigger the foot the better.