The meaning of 'carry' in a novel

Consider:

‘Why what else are you?’ returned John, looking down upon her with a smile, and giving her waist as light a squeeze as his huge hand and arm could give. ‘A dot and’—here he glanced at the baby—‘a dot and carry—I won’t say it, for fear I should spoil it; but I was very near a joke. I don’t know as ever I was nearer.’

What does 'a dot and carry' mean in this context?

"Dot and carry" is a fixed phrase common in British English in the 19th century, when Charles Dickens wrote "The Cricket on the Hearth". The phrase (also "dot and carry one") was a school name for a method used in some processes of elementary arithmetic (subtraction, division, and addition). When adding columns of tens, units, hundreds, etc, if the answer came to more than 10, one might write down the second digit and write a dot or dots to signify the figure to be 'carried' to the next column (one dot for 1, two dots for 2, etc). Dot is also a woman's name, a shortening of Dorothy. John is making a joke, as he says, based on his wife's name.