The exercise book

This is a work of fiction. My mother, Akosua Yentumi, is real, and so are the places and the work. The events and the conversations are made up.

On the morning of my dissertation defense, I packed three things: my laptop, a printed copy of my slides, and a blue exercise book with a torn cover that said “Mathematics, Form 2.”

The exercise book was not mine. It belonged to my mother, Akosua Yentumi.

She sold smoked fish from a stall at the market in Chinderi, and she wrote down every sale in that book. Date, buyer, how many fish, price. When a column didn’t add up, she didn’t erase anything. She drew one straight line through the wrong number and wrote the right one above it, small and neat, so you could still read both.

I was nine when she first handed me the book and a pencil. “Add this page,” she said. I added it and got a total that was twelve cedis short of hers.

“Again,” she said.

I added it again and got the same number. She took the book, ran her finger down the column and stopped at a 7 that I had read as a 1. She had a way of writing sevens without the little cross in the middle.

“So whose mistake is it?” she asked.

“Yours,” I said, because I was nine.

She laughed and crossed out the 7 and wrote it again, with the cross this time. That was the only time I saw her change her handwriting for anybody.

Navrongo

At university I studied actuarial science, which is a polite name for counting things that haven’t happened yet. During one long vacation, I worked in the health insurance claims unit at Tamale Central Hospital. My job was to file claims, keep the daily patient records and assign beds to people who were being admitted.

The claims came back rejected more often than I expected. One afternoon a supervisor dropped a thick pile on my desk. Most of them had failed for the same reason. A patient’s name was spelled one way on the admission form and another way on the insurance card. Abdul and Abdulai. Fuseini and Fusheini. The patients were the same people, but the system didn’t think so.

I spent two weeks matching names by hand. Then I wrote the corrections in a notebook, one line per patient, and drew a straight line through each wrong spelling. My supervisor flipped through it and asked who taught me to do it that way. I said Akosua Yentumi, my mother.

Around the same time, our community studies program sent us to Wanjagenia, a farming community near Manyoro, to run a population and housing census. We walked from compound to compound with clipboards. At one house an old man refused to give us the number of people living there until we had also counted his goats. We explained that the census was only for people. He said the goats ate from the same pot, so they should count.

We wrote the goats on the back of the form. Seventeen. I think about that form more than I should.

Kigali

After my master’s at AIMS in Kigali, I took a job as a data analyst at a bank. The first thing anyone showed me was the reconciliation backlog. It was about six months of files that someone had to match by hand, transaction by transaction, and each file took thirty to forty-five minutes.

I wrote a tool in R that did the matching. The first time it ran, a file that used to take most of an hour finished in under ten seconds. People came over to my desk to watch it run, as if it might be a trick.

One file would not reconcile. The tool flagged a single transaction that was off by a small amount, and nobody could find the reason. It sat in the queue for three weeks with a red mark next to it. A colleague suggested we write it off. It was a small number.

I printed the source records instead and went through them with a pencil. The amount had been typed with a 7 where the receipt clearly showed a 1. Someone at a branch had a way of writing sevens that looked like ones, or ones that looked like sevens. I never found out which.

I drew a straight line through the wrong number on the printout and wrote the right one above it. Then I added a check to the tool for amounts that differ by exactly six in one digit. It caught four more that year.

Boise

My Ph.D. started with galaxy clusters, the largest objects in the universe that gravity holds together. To weigh a cluster, you look at how it bends the light of the galaxies behind it. The trouble is deciding which galaxies belong to the cluster in the first place. When you look along a line of sight, galaxies that sit far in front or far behind can line up and look like members. Count them, and the cluster looks heavier than it is.

In my first project I showed that this kind of miscounting can make cluster masses look twenty to fifty percent heavier. It was the Wanjagenia goats all over again. Things that ate from the same pot, or seemed to, were getting counted as people.

Later my research moved down from the sky to the ground. I spent a summer in Berkeley turning coarse satellite maps of how much sunlight the Colorado River Basin reflects into maps sharp enough to see a single field. I spent another stretch measuring the height of sagebrush from space, which is harder than it sounds, because sagebrush is short and the laser footprint is wide. In between, I worked at the campus supercomputing center, helping other students get their jobs to run.

On weekends I played soccer with a team that called itself the Panthers. We were good. We reached the final of the second division in our league, lost that last match and finished second. In one game I had a clean shot from the edge of the box and hit the post so hard that it rang. A teammate filmed it. I posted the clip with a caption that said I almost got that into the net and would try again later. I still haven’t scored on that field.

The defense

Three committee members sat at the front. A few lab mates came, and then my friends and classmates kept arriving until every chair was taken and people stood along the back wall. More friends, classmates and family joined online, and their names filled the side of the screen next to my first slide. The projector took two tries to wake up.

I talked for about forty-five minutes about clusters, albedo and shrubs. Then the questions started. The hardest one came near the end. One committee member pointed at my slide on mass bias and asked how I knew the twenty to fifty percent came from projection and not from something else I had missed.

I said I didn’t know it for certain. I said I had held every other parameter fixed in the simulations and changed only the one that controls projection, and the bias moved with it. Then I said there was one place where my model and the simulation disagreed by a few percent, and I showed them that plot too, because I had marked it in my notes and I wasn’t going to hide it.

They asked me to step out of the room. I stood in the hallway for eleven minutes, holding the exercise book.

When they called me back in, the chair of the committee shook my hand and said, “Congratulations, Dr. Nde.”

After

That evening I called my mother in Chinderi on WhatsApp. The line was bad, so she kept asking me to repeat myself.

“So you are finished?” she asked.

“I’m finished.”

“And now they will pay you properly?”

I said I hoped so. She said she would tell my brother and my sister and the woman who sells kenkey across the road, in that order.

After the call I opened the exercise book to the last page with writing on it. It was a list of sales from a market day in a year I was too young to remember. At the bottom, in my mother’s hand, was a total with one straight line through it and the right number written small above.

I took a pen and, under her total, I wrote the date, my name and one word: “Finished.” Then I added the column again to make sure she had it right.

She did.