I found that the cutaway isn't an arc but rather a straight cut from the leading edge to the center of the slide.
Just to clarify a statement of mine in a previous reply,
MM's comment is quite correct, what I was (poorly) trying to illustrate was that the cutaway is cut as per the illustration in DD's response illustation and thus appears as an 'arc' when viewed front on (to the slide) by nature of the curve of the slide.
What I was trying (very badly!) to convey was that the cutaway is NOT at a uniform height to the centre of the slide body (don't laugh I have seen it done).
BTW, thanks David - every day is a learning day - I was unaware that TT slides were 1/32" nominated as I never had the opportunity (TTs were bonkers money at the time, if available!) - I raced with heavily modified 'smoothbore' clip fitting 32mm monoblocks - made for a two stroke!, so I started on first principles from waaaayyy over left field on a dismally small cutaway (with a big help up from Bill Thomas's knowledge - "Keeping filing until it stops 8 stroking", then measure!, thanks mate).
I then raced moderns on Miks and eventually Gardners.