When he was five, his father brought home a calculator. Not a real, live person, as calculators are in the Wizarding world, but a machine, a device. Smuggled in from the Ministry archive of confiscated equipment, it seduced him with its straight edges, simple design, and singular purpose. It had no reason to exist other than to churn out numbers, and it did this quickly and efficiently. It belonged to another world.
The Ministry eventually audited its stockpiles, and his father was rapped over the knuckles for allowing a Muggle artefact to slip through his fingers. Arthur came home in a foul mood that evening. Molly baked extra cookies, Bill buried himself in books on dragons, the twins dashed to the end of the garden to degnome, and keep out of Arthur's way, and Percy locked himself in his room, occasionally daring to peek at the numbered buttons hidden under the socks in the drawer.
It was the first item he packed when he left home.
Placing the quill on the desk, he stands and locks his office door. He makes his way back to his desk without lighting candles. All furniture in his office has a correct place, and stays there. Nothing ever moves without his permission, and Percy never gives it. A place for everything, and everything in its place. The chair squeaks slightly when he pulls it out from the desk, moving only grudgingly out of the grooves in the carpet, and squeaks again in protest, as he sits on the leather cushion. Muttering a small hovering illumination charm, he arranges the light over his desk. Then he opens a concealed compartment, and removes the calculator. In the green light, it reflects a ghostly image of himself in the small screen. This late at night, there is little real risk of being discovered with proscribed equipment. He is most likely the only person left in the department. Dedication, he discovered not long after his arrival, is a quality in short supply at the Ministry. Small, square buttons, on a small, square machine. On their own, they are worthless. Working together as part of a larger device, they perform incredible feats of mathematics. The muggle world is run by such devices, an entire civilisation held together by the magic of small, square buttons. They power cities, order food supplies, and allow men to fly without the aid of broomsticks. Percy knows there is more magic in a calculator, than in the entire wizarding world.
His father played with the calculator, toyed with its ability to do sums, without really seeing its full potential. Arthur does not see beyond his own immediate needs. He held in his hand the answer to all their problems, and did nothing more than tinker with it, to make it talk. One calculator on its own achieves very little. Hundreds of thousands of calculators move the world. Percy wants to move the world. He wants it very much. He examines the glow of the buttons, and thinks he might be glowing a little himself right now, such is his pride in his work. The Ministry will help put things right with the world, and he will be a part of that.
He closes the compartment, and pulls up the next scroll from the pile. There is still much work to be done.