CAPT OF AN LGT DIVERTED TO LAND AFTER FAILING TO PROPERLY LOCK SHUT HIS COCKPIT VIEWING WINDOW DURING HIGH ALT CRUISE FLT. NO EMER WAS DECLARED AND WINDOW WAS PROPERLY SHUT AFTER LNDG.

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AFTER PUSHBACK CHKLIST COMPLETE AND DURING PUSH; I BRIEFLY UNLOCKED/OPENED CAPT DIRECT VIEW WINDOW AND CLOSED AGAIN. DURING CLOSING; ALTHOUGH I DID RATCHET CRANK SHUT; I BECAME DISTR BY INTERPHONE COMS; AND DID NOT LOCK WINDOW LEVER. CONTINUED WITH START; TAXI AND TKOF/CLB. ALL NORMAL. REQUESTED BLOCK ALT FL410-FL430 -- APPROVED AND LEVELED OFF AT FL420. I THEN NOTICED WINDOW UNLOCKED. TRIED TO LATCH/SECURE BUT UNABLE. BEGAN NORMAL DSCNT AND RAISED CABIN/LOWERED DIFFERENTIAL; BUT STILL UNABLE TO SECURE. ALL PRESSURIZATION STILL NORMAL. HOWEVER; DECIDED TO DIVERT TO JAX TO LAND AND SECURE. DID NOT DECLARE EMER. ALL INDICATIONS NORMAL. AFTER REFUEL/NEW DISPATCH; CONTINUED FLT. EVEN AFTER AN ITEM IS CHKED/VERIFIED ON A CHKLIST; IF THAT ITEM IS SUBSEQUENTLY CHANGED; CHKLIST SHOULD BE RE-RUN; OR POSSIBILITY OF POTENTIALLY CRITICAL ITEMS HIT ON BEFORE TKOF CHKLIST. ALTHOUGH DIFFERENTIAL PRESSURE WOULD HAVE PROBABLY KEPT WINDOW CLOSED; I WAS CONCERNED THAT I COULD NOT FULLY LATCH/SECURE THE LOCKING LEVER. AT THAT POINT I THOUGHT AS A PRECAUTION THE BEST COURSE OF ACTION WAS TO LAND AND SECURE.