Fix calculation of Hz on Linux

[dbwiddis]

Fixes #623

[codecov-io]

Codecov Report

Merging #626 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #626   +/-   ##
=========================================
  Coverage     83.68%   83.68%           
  Complexity      197      197           
=========================================
  Files            28       28           
  Lines          1428     1428           
  Branches        208      208           
=========================================
  Hits           1195     1195           
  Misses          112      112           
  Partials        121      121

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