Every time machine is a one-of-a-kind device, and building one requires perseverance, ingenuity and total concentration. You will also need a clean workspace, a flat surface and the usual assortment of tools. Some of the parts and materials described in these instructions may not be available, in which case you will have to improvise suitable replacements.

Start with the sunlight's reflection off the water on the afternoon your grandfather took you out on the lake in a rowboat, the last time you saw him alive. Stabilize it with the bobbing of the ducks on the boat's wake, the breeze caressing your arms and neck, causing goose bumps, and the insistent tug of the oars in your hands when he let you row.

Attach your little sister's tears after you plucked out the eyes of her favourite plush teddy bear and hid them under her pillow for her to find in the morning. It should fit loosely, leaving room for the ringing of your mother's screams in your ears as well as the dampness of the soil on your hands when you buried your favourite toy soldier's splintered remains after your sister smashed it in parent-sanctioned retribution.

Gently screw into place the trembling of your first lover's lips as they formed a smile when you told her that you loved only her and would forever; fasten onto it the set of her jaw when you said you'd become involved with someone else. You may need to lubricate the joint with the lies you told her in the final weeks of your relationship, each encompassing the last, like Russian nesting dolls, mixed in equal parts with her blind desperation to believe you.

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Be very careful as you slip into the resulting groove the smell of the wilted get-well flowers you found on your doorstep upon returning from the ski trip with your friends after you'd told your parents you were too sick to come home for Thanksgiving. Softly tap in your mother's worried, desperate pleas in the half-dozen messages she'd left on your answering machine and connect them with the disappointment that quickly replaced anger on your father's face when you told him the truth.

Hook up the cold slickness of sweat in your palms as you signed the papers finalizing your promotion to manager. Plug in the warmth of your wife's cheek against yours when you embraced before you got into the corporate car to go to the airport for your first extended business trip, and bind it in place with the smell of her hair and the pressure of her fingers against your back.

Affix the constriction in your chest linked with the wobbliness in your knees as you stood on the boardwalk and watched your then best friend walk away after you told him it was nothing personal but you wouldn't be comfortable lending him money. The golden-pink of the sunset should slide smoothly into the smell of the ocean, the feel of salt coating your skin, and the grainy roughness of the wooden guardrail in your grip.

Install the numbness, spreading from your fingertips to your hand and up your arm, after you hit your wife on the side of her head when, during an argument that started over nothing and touched on everything, she called you a series of names no wife should call her husband. Fill in any gaps with the sound of her shocked gasp and the heartbreaking silence that followed.

Snap in the sound of the door slamming when your son stormed out of your house after you explained to him, in increasingly forceful terms, the reasons that you'd be more than happy to help pay for law school but wouldn't give a penny for a creative-writing programme. Latch onto it the flash of defiance in his eyes, the knot in the pit of your stomach and the scent of daffodils that drifted in from your front yard through the open door.

Surmount the whole thing with the tightness in the corners of your mother's mouth when you told her you would not be able to take care of her the way she needed if she came to live with you. Prop it in place with the trembling of her hands in yours, and the musty, medicinal smell of her apartment, which coated the inside of your nostrils, dried out your throat and stung your eyes.

If you've followed these instructions, and you're very lucky, you should have in your possession your very own, fully functioning, custom-made time machine, ready to take you to the moment of your choice in the blink of an eye.

If you're even luckier, you will leave it in the corner of the garage, next to the old lawnmower you've never got around to fixing, under a worn tarp, collecting dust.