Back in the days when you had to rely on celestial navigation, I sometimes went a few days with little or no chance to take a sight. By keeping an accurate log (course and speed each hour, or average for a watch) and some common sense estimates to allow for leeway and current, a DR can be remarkably accurate. IIRC I have sailed something like 300 miles and been off on the DR less than 8 miles or so.

I have to confess, I did not know it was 'ded' reckoning, but I did wonder where the 'dead' in dead reckoning came from