Investors might want to bet on Ambarella (AMBA) , as it has been recently upgraded to a Zacks Rank #2 (Buy). This upgrade primarily reflects an upward trend in earnings estimates, which is one of the most powerful forces impacting stock prices. A company's changing earnings picture is at the core of the Zacks rating. The system tracks the Zacks Consensus Estimate -- the consensus measure of EPS estimates from the sell-side analysts covering the stock -- for the current and following years. Since a changing ...