NavList:

You say why not use 1nm in 57.3nm = 1 degree instead of 1 in 60.  Why not indeed, except that would be disregarding the air navigator’s creed. When you’re bouncing along at 300ks or more, at 250 ft or less, with a tight helmet on your head, working with 57.3 is rather taxing on the little grey cells.  The aim is to get back on track before you’re long past your destination.  Therefore, when I’m just trying things out, it’s ingrained that I use 1 in 60 to come up with ballpark figures. 

On the vertical distance between mirrors, I tried something new this afternoon.  I took the telescope out of my Hughes 6” Three Circle and shone my laser pointer down the eyehole.  Then I shone it on the wardrobe, after a bit of wiggling I got two spots around 5.5cm apart.  The trouble is you need three hands to mark it up properly, so I’m waiting for Mrs P to have time to help.  DaveP