uptime --since gives varying results
As can be seen, half of the invocations claims the machine started ..:15 and half ....:16
rpi2 procps-ng-3.3.12 # while /bin/true ; do sleep 1 ; uptime -s ; done 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:16 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:15 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:16 2017-05-31 02:40:16
Edited by Anders Thomson