Why you need to buy the dip: Technician

All three major indices suffered their worst trading days since the beginning of the month on Tuesday, but one technician said that now is the time to buy.

"Each time the S&P 500 tests the 150-day moving average we've moved higher," Evercore ISI's head of technical analysis, Rich Ross, said on CNBC's "Fast Money."

Following the most recent 5 percent pullbacks in December and January, the S&P 500 recovered 6 percent and 3.5 percent, respectively, in the next two weeks.

"It would really take a break below 2030 which is roughly 2.5 percent down from here to get me more bearish," said Ross.

So if you're going to buy now, what looks attractive in this market? Ross says it's important to keep your eye on one key indicator.

"The dollar is the straw that stirs the drink here," Ross said. Crude oil, energy, materials and industrials are heavily dependent on the dollar, so it's best to avoid those sectors while the dollar remains strong, he added.

Instead, Ross said to be "overweight U.S.-centric defensives and non-commodity cyclicals, like health care, technology, consumer discretionary and small caps."