Pyramids and Temples of Gizeh, Ch. 6: Correction to Section 64

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Correction to Section 64 Summary Table:

Petrie's value (+ 179.9) for the elevation of the beginning of the Ascending Passage contains a transcription error. The correct value is + 172.9.

Proof 1:

Petrie nowhere employs the value 179.9 for this elevation.

In the last paragraph of section 39, Petrie employs the value 172.9 for this elevation.

Proof 2:

The elevation is found by h-dsinΘ, where h = the elevation of the Descending Passage floor at the pyramid entrance, d = the length of the Descending Passage floor between the pyramid entrance and its intersection with the Ascending Passage floor, and Θ = the angle of descent of the Descending Passage.

h = 668.2 (see first sentence of section 35; also, section 64 table, "Beginning of entrance.")

d = 1110.64 (see last sentence of section 38, paragraph 3: "the [Ascending Passage] floor cuts the entrance floor at 1110.64 from the [casing face]."

In section 36, two angles are presented for Θ: 26º 31' 23" and 26º 26' 42"

Calculating the elevation h for each of these angles yields 172.2 and 173.6, respectively. Neither of these values are 179.9 or 172.9. But taking the average of the two angles (as was Petrie's habit when faced with multiple values for the same measurement) yields an elevation of 172.9.

Quod erat demonstrandum.

— R.B.