If we look at Sikh Rehat 2 things should be noted. First, no alcohol allowed. Second, 4 kakkar are not allowed to leave the body, even for a second!
Let's just say the Gurus decided and gave a figure. We're allowed to consume half a glass (e.g. 250ml) of beer once a week, containing no more than 5% in alc volume. And four kakkars, let's assume Dasah Patsha stated "Four can be parted from you at a distance of 1.5 meters."
Now today, we can guess why the measurement are absolute zero. The rehat states ZERO TOLERANCE! The alcohol consumption would have been edited to "5 glass per seven days it's ok to get tipsy, Thas what Maharaj is saying" and departure from kakkar would have been "150 yards..." We Sikhs EASILY would have fooled and edited measurements!!!
The Gurus knew this. Today our actions are evidence to my opinion. So the Guru has certainly not given us any unit of measurement as we're unworthy of it.