[metrics-bugs] #34103 [Metrics/Website]: Stop rounding y axis labels with units

[Tor Bug Tracker & Wiki]

#34103: Stop rounding y axis labels with units
---------------------------------+----------------------
     Reporter:  karsten          |      Owner:  karsten
         Type:  defect           |     Status:  assigned
     Priority:  Medium           |  Milestone:
    Component:  Metrics/Website  |    Version:
     Severity:  Normal           |   Keywords:
Actual Points:                   |  Parent ID:
       Points:                   |   Reviewer:
      Sponsor:                   |
---------------------------------+----------------------
 The [https://metrics.torproject.org/torperf.html Time to download files
 over Tor graph] now displays the following labels, all using seconds as
 units: 0, 0, 1, 2, 2, 2. Better labels would be 0.0, 0.5, 1.0, 1.5, 2.0,
 2.5.

 Similarly, the [https://metrics.torproject.org/advbwdist-
 perc.html?start=2015-01-19&end=2020-04-18&p=50 Advertised bandwidth
 distribution graph] showing the median displays the following labels, all
 using Gbit/s: 0.00, 0.02, 0.05, 0.08. Better labels would be 0.000, 0.025,
 0.050, 0.075.

 The underlying issue, which we didn't fix in #33933 nor in #33066, is that
 we have to pick a number of digits for a graph which then needs to work
 for whichever scale is being displayed. In some cases this is difficult to
 do right (first graph above with measurements apparently getting faster
 over time), in other cases it's impossible (second graph above with 1st
 and 99th percentile having different orders of magnitude).

 The fix is to stop using the `unit_format` function from the somewhat
 outdated `scales` package that we're using and instead write our own
 function for formatting labels with units.

 I'm going to attach two example graphs where this went wrong plus a patch
 that I'll review more carefully tomorrow before I deploy it on the server.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34103>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online