Constant MAX_CLOCK_DRIFT_PPM 

pub const MAX_CLOCK_DRIFT_PPM: u64 = 10_000;

The clock-rate assumption behind read leases: every member’s clock (the now the host passes in) advances at a rate within this many parts per million of real time, 1 %. Message delays and scheduling pauses are unbounded; only rates are assumed. A clock that stops while time passes (a suspended host whose clock does not count the suspension) breaks it.