Foxmouth,
A technique used by some instructors in Australia is to mark the map in 'time markers'. Obviously when tracking into wind, the markers will be closer together than when tracking with the wind. And it must also be apparent that such markers are only accurate when the winds are as forecast. A change of wind or cruise technique renders the marks useless.
By marking in ten or twenty mile intervals, each mark will still be valid regardless of the direction travelled. The time to transit the marks will vary and any student with grade school math should be able to interpret ETA's accordingly!