GWX has 2 tables:
knots (nautical mile per hour) to kilometer per 1,2,4,6,10 hours.
knots (nautical mile per hour) to meter per 1,5,10,15,30, 45 minutes.
Since you usually know the speed you or the target is going you look along that row.
Knowing the time you take the longest interval below it, then succesively add the largest smaller time intervals until you get to the desired time. (or take a larger interval and subtract a smaller interval if it is more convenient/ takes less than doing additions)
7 hours + 36 minutes = 6 hours + 1 hour + 30 minutes + 5 minutes +1 minute
So you add up all those distances from the same line and get your result of distance moved at that speed over that time.
Going back from a known distance, and a time to figure out a speed is not as simple. Consider the next way to solve either of 3 unknown cases:
It is much quicker to simply learn to use that nomograph on the navigation table. Draw a line across 2 known values in the time, speed and distance scales. Then the unknown value is crossed at the correct place.
And yeah, this doesn't help much in knowing which course to move to intercept the quickest. Dantenoc's guide (linked by John Pancoast) is good for that. And I figured out
my own maneuvering sketch