Tyler pulled out his pen and carefully wrote his name. He wasn't very good at cursive, but all the text in the notebook was in cursive, so slowly his hand guided the pen. The paper was old, and incredibly smooth, so his cursive writing didn't look too bad.
Then, he had to decide how much extra weight to ask for. If he only asked for five or ten pounds, he might not even notice it - but even though he loved stories where people gain huge amounts of weight in no time, he thought that it probably wasn't a good idea to ask for too much at once. For one thing, if he wrote down '250 pounds', he wouldn't have any clothes that fit!
But he does have some clothes that are still loose, and he's got an older brother and a dad who are about his height but both bigger, so if he has to 'borrow' some clothes he can.
He wonders, his pen still in his hand, if the added weight will come in all in fat, or some fat and some muscle, or what. Another reason not to ask for too much, he thinks. If he writes down '200 pounds, very fat' he wonders if the magic of the notebook would make a difference than if he wrote down '200 pounds and muscular'.
But, part of his brain wants to be FAT! Noticeably bigger, if not huge. His big brother is just over 200 pounds, so he decides to write down, "190 pounds," after his name. That's 40 pounds more than he weighs now - very noticeable! - but less than his brother, so he can 'borrow' some of his brother's old t-shirts and jeans, if needed.
He puts the book down and sits for a minute, wondering how long the effect takes to happen. Nothing changes at first... which is disappointing, but then, is magic instantaneous? He gets up and picks up the notebook and pen, and heads back up to his room to play some Minecraft. As he sits down at his computer...