Function stagger 

pub fn stagger(
    spec: AnimSpec,
    index: usize,
    count: usize,
    spread_ms: u32,
) -> AnimSpec

spec, delayed for item index of count so the items start spread_ms apart in total: the first starts on time, the last spread_ms later. Bars rising left to right, points popping in along a line: a sequence is one spec per item, and this is the arithmetic.