The Mk-1
 
This is the only quarter mil rule. The 1:250,000 maps are used by general aviation and helicopter operators who wrote and asked for a rule that suited their navigation.  UAS squadrons were using Bulldogs back then but the Mk-1 has the outline of a Grob Tutor in the compass rose.
The Mk-2
 
Over the years, there have been several requests for a half-mil version of the Mk-1 for use on low level charts. The speed scales span 90 to 150 knots and the faster speeds also have 10" marks for use on OS 1:50,000 charts.
The Mk-3
 
This was the mainstay of the fast jet world for 15 years, developed from the initial design back in 1987.  All turning circles were at 2g.
Later, I was asked to include 3g and 4g turns at common low level speeds of 420 and 450 knots by Harrier and Jaguar pilots. 
The Mk-4
 
This was made for Tornado crews who specifically asked for certain features to be added to the Mk-3; specifically, the auto TFR turning circles and the 500/520 speed scales. 
 
Now, both Mk-3 and Mk-4 share many common features and a Hawk in the compass rose. Interestingly, some pilots asked for right turns and some for left turns! There is no pleasing some people, so now the Mk-4 turns are to the right.  The Mk-3 remains a left-turn rule!
Mk 5

Currently in Development

Standby...