abhilfe2001, I'm afraid you are just WRONG. The 180 day period does NOT get reset to zero on Day 181. You always have to look back 180 days from the present day, and check whether or not you spent 90 days in the EU in the preceding 180 days.

So, to use your example - if the OP spends a day in Copenhagen on 15 February then that day will "expire" on 15 August (give or take a day - I haven't actually counted). The ten days in April will expire in October. The ten days in May will expire in November. And so on.

The 180 day period will NOT restart on 15 August.