After my 3rd and 4th glider solo flights, I was putting the aircraft away and getting it tied down, and both static ports were still taped. Obviously not untaped in the preflight.
This explained the crazy lag I had noticed on the altimeter. It had lagged about 10 secs behind where I actually was, and slightly upset my initial pattern entry, but I had disregarded it and flown base & final visually like I've been taught.
That was a bit embarrasing, and potentially dangerous for someone flying 'on the gauges'.