Runaway Gun's explanation seems to be the solution that will get you to the turning point. I remember learning this in RAF flying training in the mid 80s and it was known as the New Track Reference method. The disadvantages were that it took a while to calculate and second, it did exactly what it says on the box and gave you a new track. Often, regaining track was the best policy for several reasons.
A few years later, when I became an instructor, I was pleased to see the NTR method ditched in favour of the Standard Closing Angle technique. Based simply on the 1 in 60 rule, you applied an angle (the SCA) to regain track and flew this new heading for as many minutes as you were miles off track. The angle you flew was based on your groundspeed. At 60 knts, you flew 60 degrees (1 in 60), 120 knts = 30 degrees, 240 knots = 15 degrees, 300 knts, = 12 degrees, 420 knts = 7 degrees. Its basicly 60 divided by as many miles a minute you are doing.
So at 90 knots, your standard closing angle would be 40 degrees (60 divided by 1.5). If on a heading of 360, at a check point you noticed you were 2 miles right of track, if you steer 320 for 2 minutes then come back onto your original heading, you will be back on track. As Tinstaffl mentions, you do have to apply a correction to prevent it happening again. Decide whether was it a once only error (avoiding weather/inaccurate flying) which means no correction, or a persistant error (wrong drift applied/wind different to forecast) then a correction is required.
The advantages of this method is that it's simple, easy to apply and quick - as you will have worked out the SCA for your speed at the planning stage. Once you have recognised you are off track, the calculation can be made in seconds and applied immediately - and you have the added benefit of regaining track with all the attendant advantages. The disadvantages are that the heading change can be a bit extreme with problems if you miss the time you need to turn back onto track, and the gound track increases a bit with a resultant change in the timing for the leg. To alleviate thes problems, you can change the values slightly. On one type I instructed on which flew at 90 knts on NAVEXes, we used 20 degrees for 2 minutes per mile off track.
It works very well, and it's suited to the high workload low level
environment in military flying and the PPL sunday afternoon trip to another airfield for tea and stickies alike. And it's well within the parameters of the KISS (Keep It Simple Stupid) philosophy I like to apply to my working life!