```rust
#[test]
fn checksum() {
    // From the manual, TempleteNum
    let part1: u16 = 0x01;
    let part2: u16 = 0x00;
    let part3: u16 = 0x03;
    let part4: u16 = 0x1D;

    let mut checksum: u16 = 0;
    checksum = checksum.wrapping_add(part1);
    checksum = checksum.wrapping_add(part2);
    checksum = checksum.wrapping_add(part3);
    checksum = checksum.wrapping_add(part4);

    assert_eq!(checksum, 0x0021);
}```

Wow. That passes. It takes it a byte at a time.