After tripling in the past year, Nvidia has analysts throwing up their hands

Shares of Nvidia hit a fresh record high in early Tuesday trading, the 69th record high logged by the stock in a year's time. And with Nvidia stock now more than tripling in value over the past year, some analysts tasked with covering the stock are left scratching their heads. "I have been making a valuation call on this stock for a long time (and clearly have been wrong)," Ruben Roy, MKM Partners analyst and managing director, wrote Monday in an email to CNBC.