You can't think in months. You have to think in days.
The 180 day clock is constantly moving.
Let's say you stay 60 days and leave. In the next 120 days, you can stay 30 more days.
The 180 day rule doesn't reset. It is constantly moving.
Let's use months just as an example. Assume in this example that every month has 30 days.
You arrive in the beginning of January and leave at the end of February. That's 60 days. You still have 30 more days until the end of June. You return the beginning of June for your 30 days. But at the beginning of July, if you go back 180 days, January has disappeared and you've only stayed 120 days in the previouis 180 (Feb and June). You get an additional 30 days. (July) In the begining of August, February has disappeared and you get an additional 30 days. But now you've stayed 90 days (June, July, August) and must leave until at least the beginning of December. (June-November is 180 days in my example.)
An entire month doesn't disappear at once. So, using my example of days, on August 1, February 1 would go. On August 2, February 2 would go.)
So, to answer your question, you could return on day 150 from your first entrance into Schengen and stay for 60 days.
However, none of us suggest you do that and always give yourself a few days leeway just in case of delays. Immigration officials don't care that your flight was canceled or you were sick or whatever. Overstaying your stay in Schengen can mean a hefty fine and exclusion for up to 10 years.
In reality, months have a different number of days which is why I suggest you don't think in months. Arrival days and departure days count towards your 90/180.