Abs to reckon with

Inspired by the large fitness ball in Jenn's apartment, I decided to replace my chair in my office with a fitness ball too. As long as I sit behind my desk, I reasoned with myself, there's no reason why anyone should even notice.

So come Friday lunchtime, I dragged MetroHom to the sports store near work. Headed down to the fitness ball section in the basement. And looked in mild panic at the rows full of deflated, packaged balls. How one can reduce an entire fitness ball to 3 cubic inches in size I will never know.
"Erm, okay," MetroHom glanced at me, trying to decide which one to go for, "55cm, 65cm, or 75?"
"I have NO idea. What do you think?"
"How tall are you?" he asked.
"Erm, 110 cm I think." I have no idea where that came from, other than an absolute inability to translate between the American and metric systems.
"Three feet?? You're three feet tall??"
"Okay okay FINE I don't know!"

In the end my greed got the better of me. I picked the largest of the balls, 75cm. ("I think that might be almost your height," MetroHom snickered.)

Finally, we were back at work. I quickly pumped up the ball, and much to my delight (and luck) it was exactly the right height. So gone is the era of the office chair. From now on, it's going to be all straight backs and taut abs.

Over the course of the afternoon (after only a couple of mishaps), I got quite used to sitting on a ball instead of my normal chair. And as long as I sat behind my desk, facing the door, I didn't think anyone would even notice the difference. But then MetroHom popped his head into my office as he passed on his way to the kitchen. "You do realise you're bopping up and down as you sit, don't you?"
"Oh." I wonder if that detracts somewhat from my credibility at work.