The way I was taught is to lock your front brake, turn your bike around keeping the front wheel in contact with the point you stopped. Ride back following the same exact route and stop at a point on your course, after you have ridden an even number of counts. (1000,2000/5000 etc.) Then double that number and add to your remaining layout counts and continue. In most cases, you would only have to increment the 4th or 5th digit. Example: you have ridden approximately 1/4 mile off course when you say to yourself "Ah Shucks" and your counter reads 123456. Measure backwards let's say 5000 counts to 128456. Since you rode 5000 counts off course and 5000 to get back, just increment the 5th digit by 1 for all remaining splits. Of course it depends on how far off course and how far into the measurement you are. If I found myself a 1/2 mile or more off course I would probably ride back to the last split I marked and recalculate the remaining points.