There is no clear course to the past but only a kind of dead reckoning.

I haven't but a small notion where we are, going by dead reckoning.

But do not think his dead reckoning can be very accurate.

In the cloud they go by dead reckoning from their last known position.

But I knew his dead reckoning couldn't be exact in these conditions.

At the present moment, by vague dead reckoning, we are two hundred miles east of them.

He took a course reading and prepared for another hour or more of careful dead reckoning.

This is known as dead reckoning when used more formally.

So he tried dead reckoning, which was impossible due to the wind.

Clearly, something better than dead reckoning was needed to find the way in dangerous waters.