Jack arrives home from university even though it’s not yet spring break. He’s thinner than before he left, his elbows pointed like the sharp angles of the engineering caliper he carries everywhere. He says if something can be quantified, then it’s real.

“Sometimes, I’m not sure I’m real,” he whispers to me when Mom and Dad aren’t around.

I’m thirteen and don’t have a clue what he’s talking about, but I’m happy he’s at least speaking to me. Sometimes, when we’re alone, he lifts the caliper to his temple.

“Bang,” he says, canting his head grimly, and laughs.

“What’s wrong with you?” I ask, but that only makes him laugh harder, only it’s not the kind of laughter that makes me want to join in.

“Zero point error.” He slides the measuring jaw along the ruler-like scale, like I’m supposed to know what he means.

“You’re an error,” I say, except I don’t mean that and want to take it back the moment I say it.

Jack doesn’t sleep anymore. He says it’s the new pills. He measures everything in the house: the diameter of Mom’s knitting needles, the arc of smoke from Dad’s cigars. He scribbles numbers on sticky notes, pastes them on the spines of The Theory of Everything and An Astronaut’s Guide to Life on Earth, sticks one on the brass pendulum in the hallway grandfather clock, posts another on a chunk of gruyere in the fridge. When he finishes the calculations of every item in the house, I find him outside under the sycamore, the caliper pressed against the length of a dead robin’s leg. He moves it to the width of its folded feathers, overlapped like origami. Scribbles the number on a yellow sticky note.

I catch him calibrating the distance between the faded scar on his wrist and his fingertips, the width of his big toenail, the trajectory of a raindrop as it slips down the window. At night, I wake to the soft rasp of metal against metal, the flint-edged caliper hovering above my skull. 

His cheeks glow like a fever pitch in the light from the hallway. “Can you still see me?” he asks.

“Of course, I can,” I say, and push his hands away. 

“Don’t let me disappear, Katie,” he says. Gently, he presses a sticky note to my forehead. 

He doesn’t come home Thursday. Friday. Mom and Dad grow taut like an elastic band ready to snap. Eyes red-rimmed, they sit at the kitchen table with their untouched rye and Cokes and whisper about the average age of onset for schizophrenia, the missed appointments and missed meds. I find out zero point error means the calipers don’t read zero with the measuring jaws closed. Readings will be skewed. Nothing will make sense.

I search Jack’s room for the caliper, but it’s gone. 

Blue, yellow, and pink squares rainbow the living room, kitchen, and bedrooms. Mom and Dad pull the notes off, one by one, and toss them into the bin.

“We shouldn’t encourage this,” they say.

I find a sticky note in my Sketchers, one tucked between the pages of my math textbook, another impaled on the tip of a hanger in my closet.

Years later, my teenage son asks, “Can you see me, Mom?” and my heart shatters. I take the old caliper, rusted with disuse from the dusty box of Jack’s things. “If we can measure something, it’s real,” I say, and help him measure every item in the house, the softening curve of my jaw, the length of his hands, so like his uncle’s, until everything is festooned in yellow, blue, and pink.