This week I had to do a sum.

I have always considered myself quite good at maths. I achieved 100% for a maths test once. Mental arithmetic was never a problem, and even logarithms were a challenge I enjoyed.

But that was a lifetime and more ago. Before calculators and cell phones meant we didn’t have to think beyond pressing a few buttons.

Even so, this week, I thought I would manage my sum without a problem

I have made a few changes in my new home. Scattered throughout my small garden were some beautiful, weathered paving stones in random paths. I didn’t want paths, but the stones were too pretty to sell, so with the help of a couple of friends I decided to build a small patio outside my study window. A round table, two chairs and a bench made it an ideal place to spend a warm summer’s evening or, later, a sunny winter’s lunchtime.

So we laid the stones out, spacing them with care so they stretched across the top of the garden. I felt independent and capable as I went out one morning, armed with my tape measure.

First I measured the patio. Then I measured each stone and counted them.

By my reckoning, the area of the patio minus the area of the stones would give me the area of the gravel I needed to buy to fill in the spaces between any two stones.

Fine.

I calculated the area of each stone and multiplied that by their total number. Then I calculated the area of the patio.

And did my subtraction.

No problem.

But I realised, as I was working that I would need a cubic measurement, not a square one. So out I go with my tape measure again and measure the depth of the stones.

And I multiplied this figure by the square footage of gravel I needed (sorry square metrage doesn’t sound right – so I’ve used footage).

What a strange number!

I looked at it and looked again at my calculations. There was definitely something wrong with the decimal point. I tried again. Nope, still not right. I wracked my brains. How did you know where to put the decimal point? After a couple of tries I got it right – I think. For each place behind the decimal point there would be a corresponding place in the answer. Wouldn’t there?

Eventually I managed to reach an answer I thought was about right. But I also thought it would be a good idea to take my calculations to the suppliers so I could get them to check. I did not want to have to return for more – nor did I want to have to find a home for far too much gravel.

I felt quite pleased with myself. Even my friend was impressed.

Digging in my bag for my notes as we arrived, we told the man behind the counter we needed to buy gravel.

“Fine,” he said, “How many kilos do you want?”

‘Nuff said.