Function nice_ticks 

pub fn nice_ticks(min: f64, max: f64, max_count: usize) -> Vec<f64>

Axis ticks on a 1-2-5 step inside [min, max]: at most max_count, at least two, every one a round number at its step’s precision, so an axis reads 0, 10, 20, 30 instead of 0, 11.5, 23, 34.5. A range too narrow or too odd for two round ticks gets its two ends.