“You know about RDF?” John said.
“I type all of Mr. Churchill’s memos and letters—I’d have to be insensible not to. I also know queuing theory, differential equations, and cryptography,” she said with a smile.
She was gratified to see John’s eyes widen.
John sat looking at Maggie for some time, head cocked to one side. “Do Mrs. Tinsley and Miss Stewart know?”
“With all due respect, Mrs. Tinsley and Miss Stewart don’t have degrees in mathematics.”
John was silent. Then, “Really? My calculations are off?”
“Look, it’s simple, really,” Maggie said in her best Aunt Edith lecture tone, pulling out a piece of scrap paper to illustrate the point. “If you’re using the radar equation, all the variables must be in place before solving for the position of the German planes.”
“Yes, yes, I know that,” he said, getting up and beginning to pace. Maggie could tell he was reworking the problem in his head. “So then why are the numbers off?”
“There’s an additional step. You’ve assumed that F equals 1, which means that you’re calculating in a vacuum. You see, it’s not just an abstract problem, you’re also dealing with the real world, where things get a little more complicated.”
“Is that a fact?”
Maggie ignored him. “You need to figure in a few additional variables to calculate F: the bend of the earth’s surface and the density of the refraction due to air layers at different altitudes. You also need to know the plane’s ground speed—which is different from airspeed, or what appears on a pilot’s gauge—as well as the wind speed and direction, the relative humidity, and altitude at sea level.”
“Oh,” he said, stopping his pacing. He scratched his head. “Ah.”
“You can just compensate for the additional factors. For example, if you assumed that density decreased linearly with height, and used the arc of a circle from London to Berlin …” Maggie went back to the scratch paper, pulling out her beloved Faber-Castell slide rule from the desk drawer, and made a few calculations.
“You’ve got one of those?” John whistled between his teeth. “That’s a beauty.”
What did he think I used? My fingers? “Graduation present.” Of course, Maggie never thought when Aunt Edith gave it to her at commencement that she’d be using it to figure out enemy plane trajectories.
“That’s quite impressive.” He pulled up a wooden chair, the legs scraping over the linoleum floor, and sat down again. He leaned in to look at it, giving off the faint scent of shaving soap and wool.
“Thank you.” It took her a few minutes to look up various numbers and make calculations. “And voilà! A corrected answer.”
He put his finger to the side of his forehead and started to massage his temple. It was clear that he was out of his depth. “I’ve got to get this in by the end of the day. I’m hopelessly behind.” He looked at Maggie with trepidation. “I studied classics at university—don’t actually remember much maths. I—I don’t suppose you’d, ah—”
“I’d be delighted.” Maggie picked up his memo. “Look, everything else in the report is fine; I’ll just redo the calculations, and you’ll be set.”
“Thank you, Maggie.”
You’d better thank me, she thought, inordinately pleased, as he went out the door. But she was soon absorbed in the sheer joy of math again as she worked through the problems. How she’d missed it.
An hour or so later, Maggie was outside John’s office, about to drop off his corrected memo as well as a data table for him to use in the future, when she heard voices. “Says she knows about RDF?” It was Snodgrass.
“She does know about RDF, sir. And about queuing, cryptography, you name it.”
“She does, does she?”
Maggie strode into the office, chin high. “Mr. Sterling. I wanted to drop this off for you. The numbers we discussed,” Maggie said, looking directly at Snodgrass. He sat in the chair across from John’s desk, a cigarette in one hand and legs crossed at the knees.
John stood up and reached out for the papers she offered. “Thank you, Miss Hope.” He looked at the calculations. “Mr. Snodgrass, this is what I was talking about,” he said, handing the papers over.
“Good, good,” Snodgrass said without looking at them. “Better get some of your maths books out and refresh that memory of yours, old boy!”
John looked at Maggie, then back at Snodgrass. “I believe Miss Hope would be able to assist Mr. Greene in these calculations far better than I.”