Script Analysis - Fundamental Error

I went back to my Script Analysis today, and discovered, much to my horror that I've made a fundamental error.

I was looking at the individual letters, and happened to look at the ductus shown in the Historical Source Book for Scribes. Much to my suprise, the x-height stated was 5, not 4 pen widths.

I went back and measured the blown up reproduction in the Stan Knight book. My measurement of the pen width = 2.25 mm, not 3 mm as I'd originally measured. I have noticed, over time, that you must angle the ruler absolutely correctly to the angle of the stroke or you'll get varying answers. (well, doh!)

So, back in Script Analysis - pen width, x-heightthe commentary

"Thankfully, Stan Knight says that his blowup is 150% of the original's size. Somewhere I needed a clue of how big the original actually is. You never know by how much the reproductions have been re-sized just by looking, and this told me.
So I needed to multiply everything I measured in the Stan Knight blow up by 0.667.

Pen width (measuring on a wide part of an O) = 3 . So, if it's 150% the size of the original I need to multiply it by 100/150 or 0.667 = 2 mm.
That is the pen width used in the Bedford Hours and Psalter.

I measured the x-height - not between the lines drawn inbetween which the text is floating (I'll do that later) but the height of a,c,e,on,m etc. (normal 'x-height). It came to 11 mm on this reproduction.
Again, multiplying by 2/3, I got 7.3 mm, which is what the x-height should be on the original
So, x-height at 7.3 mm, with pen width at 2 mm, that gives up approximately 4 pen widths for the x-height."

SHOULD read

Pen width (measuring on a wide part of an O) = 2.25 . So, if it's 150% the size of the original I need to multiply it by 100/150 or 0.667 = 1.5 mm.
That is the pen width used in the Bedford Hours and Psalter.

....
Again, multiplying by 2/3, I got 7.3 mm, which is what the x-height should be on the original
So, x-height at 7.3 mm, with pen width at 1.5 mm, that gives up approximately 4.8 (ie 5) pen widths for the x-height.

Oh. Well - mega bugger!

I'm not going to torture myself by re-sizing the other pages I've got to represent the actual size of the page, and measuring the x-height.

I've been happily looking at my photocopies and basing adjustment calculations assuming the nib width was 2 mm. Which means that where I look at where the letters that have ascenders and descenders (b,d,f,g,h etc) in the entries Script Analysis - Float, Ascender and Descender Heights (Backhouse) and Script Analysis - Float, Ascender and Descender Heights and measure how they fit against the ascender and descender heights of letters like d and t are all slightly incorrect.

I drew nib ladders on those reproductions using a pen with 2 mm nib width and fitted in 4 nib widths on the ladder.
At 1.5 mm nib width, the ladder is 0.5 mm shorter.

Perhaps it isn't a problem. Saying "and the right hand side of the 'h' finishes 1.5 mm below the baseline" and "the t finishes 0.5 mm above the waistline" won't be that inaccurate. I'm going to have to go back and check, tho.
Not to mention the a/d heights being wrong.

I think some of this comes down to not reproducing the various pages from the books to exactly the 'real' manuscript size.

The ruled up guidelines in Script Analysis - Drawing up the Guidelines are also incorrect. I've re-measured the ascender/descender height in the Stan Knight blow-up and come up with 2 nib widths. Michelle Brown/Patricia Lovett come up with 1.5 nib widths, but actually use 2 nib widths in their ductus. Yes, I am working in 'absolute' measurements at the moment (eg saying 0.5 mm instead of saying 1/4 pen width). I'll translate these references to pen width proportions later on.

Anyone got a brick wall handy?
This is meant to be a learning process and I'll only learn by making mistakes.
But Ouch!
*insert swear words here*