PHILADELPHIA — A Philadelphia father put the city’s signature sandwich to use in a whole new way: measuring his baby’s size in cheesesteaks.

Philly.com reports Thursday that computer programmer Brad Williams used a foolproof system he calls “Cheesesteak for Scale” to measure the growth of his son during the child’s first year in 2015.

It started when he noticed his 2-week-old, Lucas Royce, was about the same size as a cheesesteak he’d brought home. So Williams snapped a picture of the sandwich next to his newborn and the tradition was born.

Every month for the next year Williams and his wife would buy a cheesesteak to track their growing boy .

He says babies and cheesesteaks are quite similar. He says they are warm and cuddly when wrapped up “but once you unwrap them, expect a huge mess.”