the input compression value; should be >= 1.0; this
will control how aggressively the t-Digest compresses data together.
The original t-Digest paper suggests using a value of 100 for a good
balance between precision and efficiency. It will land at very small
(think like 1e-6 percentile points) errors at extreme points in the
distribution, and compression ratios of around 500 for large data sets
(~1 million datapoints). Defaults to 100.