Is OK/NOK better than "fail/success"

My team is discussing how we should indicate, in a logbook, whether a specific action ended with success or not. I started putting it like 

timestamp | action name (fail)    | description
timestamp | action name (success) | description

One of the team members suggested replacing fail/success with OK/NOK: 

timestamp | first action name (OK)    | description
timestamp | 2nd action name (NOK)     | description

I wouldn't mind such a detail, if he didn't say it would improve readability. I doubt it:

  1. OK and NOK correlate to 66 %, so arguably when quickly going through a lot of text, it is probable to confuse NOK for OK. To the contrary, fail has 0 correlation with success.
  2. fail has a varying letter height, which success doesn't, making them look very different.

Am I thinking in the right direction? Is there any resource where I can read about such details? I believe something like this should be very well known in the area of cockpit or nuclear power plant control room design.

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