All righty, this is a very geeky post.
I have read in a couple of places that one way to count while you’re practicing, e.g., six ujjayi breaths followed by normal breaths, is to use your finger joints.
Open your hand and look at the finger joints. Your fingers have three each, for a total of twelve joints. Use your thumb to touch the joints and use them as counters. So on your first breath, put your thumb on the bottom joint of your index finger. Second breath, thumb on the middle joint of your index finger. Third breath, thumb on the top joint of your index finger. And so forth.
Why this is cool: English and Sanskrit and many other languages are in the Indo-European language family. Evidence has been used from many of these languages to reconstruct proto-Indo-European, a prehistoric language spoken as far back as the 5th milleneum BC. This language and some of its descendants used a base twelve counting system, instead of our base ten system. The base twelve system arose from the same knuckle counting I’ve described here. So this is an ancient way to count on your hands.
(Linguistic trivia: Ever noticed that the words for the numbers 11 and 12 don’t follow the pattern of the words for the other numbers between 10 and 20? That pattern is ‘three-ten’ = ‘thirteen’, ‘four-ten’=’fourteen’, etc. ‘Eleven’ and ‘twelve’ don’t break down into two parts that way. That’s because they’re remnants of the base twelve system.)
Practice Notes 
Geeky and very cool.