When I first noticed this I contacted the Petrie museum who have a typed copy of the original manuscript. The error is also there.

Very interesting information and also interesting that this misprint made it into the revised and condensed Second Edition.

I suspect that not many people were using the figures in the same way that they are today.

Now anyone with a computer and a basic drawing programme can use Petrie's figures and this sort of misprint shows up straight away.

AutoCAD and similar programmes has made it too easy. A few key presses are no replacement for the hard work and care that Petrie took over his survey.