private double adjustByConfidence(double headroom, Instant now) {
        return ( (headroom -1 ) * Math.min(1, averageQueryRate(now).orElse(0) / queryRateGivingFullConfidence) ) + 1;
    }
Headroom values are a multiplier of the current query rate.
Adjust this value closer to 1 if the query rate is too low to derive statistical conclusions
with high confidence to avoid large adjustments caused by random noise due to low traffic numbers.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/autoscale/ClusterModel.java