Why does Caponsacchi count his fingers in “The Ring and the Book”?

Question

In book VI of Robert Browning’s The Ring and the Book, Giuseppe Caponsacchi tries seducing two women of Arezzo with love-poetry, but he is disappointed with the results:

                            Sirs, ere the week was out,
I saw and said to myself “Light-skirts hides teeth
“Would make a dog sick,—the great dame shows spite
“Should drive a cat mad: ’t is but poor work this—
“Counting one’s fingers till the sonnet’s crowned.
“I doubt much if Marino really be
“A better bard than Dante after all.”

What is the meaning of the line in bold? Does ‘counting one’s fingers’ mean ‘counting on one’s fingers’? But if so, what is he counting? Lines of verse? Or does it mean something like ‘twiddling one’s thumbs’, that is, being idle and bored? Neither meaning appears in the entry for ‘count’ in the OED.

Update I think Peter Shor is right that Caponsacchi is counting syllables, but here are three citations for the ‘idle and bored’ meaning:

1825   Thomas Dick Lauder Lochandhu 118   with nothing to do but count one’s fingers.

1850   Esther Copley Cottage Comforts 206   they shall do it, while I sit still and count my fingers.

1855   Harriet Parr Gilbert Massenger 75   with nothing to do but count my fingers and remember Bible stories.

Answer 1

He was probably counting on his fingers, trying to ensure that there were exactly 11 syllables in each line.

In the 19th century, counting one's fingers seems to have often meant counting on one's fingers. There are a number of instances in Google books where one can see this. For example, from 1885, less than 20 years after Browning wrote The Ring and the Book, we have

When he forgets the combination, 9 and 8, he does a very natural and proper thing by counting his fingers. But he is not adding when he does it. He must learn to name the result without the use of objects.

I think Caponsacchi was probably counting syllables in each line, rather than lines in a sonnet. The most common poetic meter in Italian is the hendacasyllable (endecasillabo), where each line has 11 syllables, coincidentally just one more than the number of fingers. Counting to 11 fourteen times is much more tedious than counting to 14 just once. Further, the rhyme scheme ensures you have 14 lines, while the only thing that will ensure you have 11 syllables in a line (besides an innate sense of meter) is counting.

This also shows that Caponsacchi isn't a good poet. I expect that good Italian poets (like good English poets) have a good sense of poetic meter, and only very rarely actually need to count the number of syllables in a line to make sure they've got it correct.