Problem diagram.
What is the value of the endgame play at A?

Source:
Endgame Calculation
Go World #1, May-June 1977, pp. 34-35

Solution follows    (or click here to download SGF)

Black plays first.
The endgame value of Black 1 is: how many MORE points does Black have plus how many FEWER points does White have, than if White had played at 1 first. I can wait while you re-read the previous sentence.

So the first step is to see what happens when Black plays first. After Black 1, White has only a small gote play on the top, so White almost surely will play elsewhere. Therefore, Black's sente hane at 3 will be Black's privilege later. White 6 exhausts the local plays.

Use this diagram result for reference against the next diagram, in which White plays first.

White plays first.
The next question to answer is what the position would most likely look like after White plays 1 first.

After White 3, a White hane would be gote, because Black would just block and White would have to connect. So later, Black would most likely have time to descend at 4. White 5 exhausts the local plays.

In the first diagram, Black has 3 more points of corner territory than in this diagram. While in this diagram White has 4 more points along the top plus the 1 captured stone than in the first diagram.

So Black 1 in the first diagram is worth 8 (3+5) points.

Simple, eh? Of course, endgame plays can become much more involved, but the principle shown here still forms the basis of the calculations.

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