The U-jagd tools mod includes this sliderule and instructions for getting speed with the constant bearing method - it also includes instructions for getting a speed estimate on an intercept course when you DON'T have a constant bearing too - although in this case you do also require a rough range estimate too

Someone, i forget who (could be h.sie) made a mini-mod adding it to OLCGUI

http://img136.imageshack.us/img136/1...derule1mw2.jpg