twentyelevens
I've just recently did flight planning and it is still fresh in my mind.
If you have current Treu OAT then line that up with the DOUBLE ARROW mach index in the true airspeed window.
ie temp -46 then place the arrow on it, then read from inside grey scale as Mach No, ex if M0.8 then 80 on grey to the outside scale which willl be your TAS. Roughly 480 Kts.
If you have an indicated OAT ie -4 for FL310 (pretty warm) then line up the Mach no with the small arrow. Use the green rotating lie CT 1.0 and line it up with the spiral line in the Mach No window and read your TAS from that. Again with a M0.8 and IOAT of -4 TAS should roughly be 481 Kts.
Hope this helps
And enjoy
ITS