It’s possible to cheat, but (1) why bother? You’d only be cheating yourself; (2) how do you know to cheat if depression has snuck up behind you, and that sneaking is what you want to be automatically alerted to because depression doesn’t tell you it’s depression it tells you that you suck and it’s all your fault and you deserve it.
An objective measure, like weight or hours of sleep or time to run 5km doesn't have this property.