@Override
    public Metrics toDay() {
        HistogramFunction metrics = (HistogramFunction) createNew();
        metrics.setEntityId(getEntityId());
        metrics.setTimeBucket(toTimeBucketInDay());
        metrics.getDataset().copyFrom(getDataset());
        return metrics;
    }
Histogram includes data range buckets and the amount matched/grouped in the buckets. This is for original histogram
graph visualization
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/meter/function/HistogramFunction.java