HN and HJ

[framer]

Why is the abbreviation for " hours of night " HN while the abbreviation for "hours of day" is HJ ?
Is it something to do with the French language?
Thank you in advance :)

[framer]

Ah thank you , makes sense now.

[mustafagander]

There's quite a bit of French in aviation. Hangar, aileron. GR for hail just for a start.