C of G - here you go
1. Plot the position of the ship at the time of takeoff and measure the angle of the line of constant bearing from Base and the distance from Base to the ship’s position.
2. Using the square scale of the computer (the lower half of the card) set and mark the W/V using an X, then set the ship’s heading under the true course pointer on the whizz-wheel and mark the ship’s speed straight down from the W/V mark using ┴ or some other mark different to the W/V to avoid confusion.
3. Set the TAS under the centre circle and set the line of constant bearing from Base to ship under the true course pointer.
4. Adjust for relative drift using the ship’s marker, not the W/V.
5. The heading outbound will now be under the true course pointer.
6. The groundspeed outbound will be at the W/V mark.
7. The closing speed to the ship will be at the ship’s mark.
8. Time to intercept is a question of dividing the distance to run by the closing speed.
Hope this helps.