basically a single byte of information can signify any number between 0 and 255. there are 8 bits in a byte, each of which the computer reads as either a 0 or a 1. since there are two possibilities for all 8 spots, there are 256 (2^8, or 2x2x2x2x2x2x2x2) possible combinations of 0s and 1s in any given byte.

if you add a second byte, you can now make numbers up to 65,535 (256x256 = 65,536, and since we can also indicate 0, the maximum value is one less).

mysql has 5 integer types that we can assign a field in the database, each of which is a different number of bytes. there's tinyint (1 byte: 0-255), smallint (2 bytes: 0-65,535), mediumint (3 bytes: 0-16,777,215), int (4 bytes: 0-4,294,967,295), and bigint (8 bytes: 0-18,446,744,073,709,551,615).

we just changed onhand from an int to a bigint.