func (hc *histogramCounts) observe(v float64, bucket int, doSparse bool) Inside `histogramCounts.observe`, for **classic buckets** it simply does `atomic.AddUint64(&hc.buckets[bucket], 1)`. For ...
Classic histograms use pre-defined upper bounds (e.g. `DefBuckets = {.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10}`). On each observation, the bucket index is ...