$ perl -MTime::HiRes=time -le 'while () { $a=time; print $a, " ", $a-$b; $b=$a; sleep 1.01 }'
Use of uninitialized value $b in subtraction (-) at -e line 1.
1579951233.92519 1579951233.92519
1579951234.92536 1.00017690658569
1579951235.92573 1.00036287307739
1579951236.92672 1.00098919868469
1579951237.93894 1.01222395896912
1579951238.95456 1.01561999320984
1579951239.97017 1.01561403274536
1579951240.98579 1.01561689376831
1579951242.00141 1.01561808586121   !!!!
1579951243.01703 1.01561903953552

$ perl -MTime::HiRes=time -le 'print $Time::HiRes::VERSION'
1.9741

$ perl --version

This is perl 5, version 26, subversion 3 (v5.26.3) built for x86_64-cygwin-threads-multi
(with 7 registered patches, see perl -V for more detail)

Copyright 1987-2018, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl".  If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.