The Measurement Shop, at Elephant and Castle Shopping Centre

The credit crunch, whatever else it ends up doing to the the arts, has been great for pop-up theatre - all those boarded-up shops provide ready-made performance spaces, with a set of associations that are, if not exactly better than those of a purpose-built theatre, certainly different.

So far this year, I've seen a tribute to Hoagy's Nest an imaginary '70s children's TV show, in Brixton Market, and debbie tucker green's Random in the Royal Court's Theatre Local at the Elephant and Castle Shopping Centre. Currently running next door to the Court's temporary space (if you're reading this before 6pm on Thursday 5th August) is The Measurement Shop, an installation/performance by the Tangled Feet Theatre Company.

The project explores different aspects of the idea of measurement - in the shopfront, you deal with the more literal side, getting measured and weighed, totting up the hours of sleep you had, the time you spent on a mobile phone and the number of times you've been in love. We were asked to think of two things we measure every day - I came up with money on my Oyster card and coffee into a mug.

At regular intervals, visitors are ushered into the back of the store for a performance, where the ideas get more abstract. We see the life of an imaginary character told entirely in terms of weights and measures, from being weighed at birth to being measured for a coffin. A dance piece deals with the measurement of recovery, we're taken into a darkened room and hear a talk on the criteria by which we measure progress, and finally, in the last room, asked to give our own idea of the hardest measurement of all, that of happiness.

It was a thought-provoking show, especially the last part, and started me wondering about the whole concept of measurement, and evaluation. When coming up with the two things I measure every day, I started with things for which there is an objective, or at least agreed, standard - money (on my Oyster or in my wallet), time (the minutes before I have to get up) and food (the number of eggs into a saucepan). But it's true that, like most people, I often try to measure things that aren't so easy to quantify - happiness, success, my own worth (and, like most people, I'm generally unsatisfied with the measurement, certainly of those three).

In some ways, I'm envious of people who judge themselves in terms of money or social status - at least they know what game they're playing. The rest of us have to make up our own rules - deciding whether we're leading a worthwhile life by standards that we have to set for ourselves - a fellow director once told me that the two criteria by which he judged his success in the world were 'standing ovations and female orgasms'.

One of the stranger responses to Vince Cable's recent proposals for a Graduate Tax was a letter in the Standard protesting that this would penalise people who opted for courses that led to a larger income. The writer's assumption seemed to be that making money is not just expedient, but actually virtuous. I find myself wondering mischievously if part of the appeal of monetarism is that it eliminates existential angst - if earning money is the central virtue, you're saved the trouble of wondering whether you're living a worthwhile life. It's like the more authoritarian kind of religion, only with solvency occupying the place that obedience does for the devout. The rest of us have to work out how to measure our own lives - a bit trickier, but, in the end, a little more adult.