What is the difference between valency and oxidation state

1. Valency is the combining capacity of an element whereas O.N. is the charge on an atom when combined with other atoms.
2. Valency is only a number and does not have +ve or -ve sign whereas ON is a charge and have +ve or -ve sign.
3. Valency can’t be zero whereas ON can be zero. e.g. C in CH2Cl2.
4. Valency is always a whole number whereas ON may not be a whole number. e.g. Fe in Fe3O4 (8/3)