Jerome Powell’s key task as the next Federal Reserve chairman will be finding a “magical neutral interest rate,” bond manager Bill Gross said.

That rate is one “which keeps inflation at 2 percent or lower and growth at 2 percent or higher,” Gross, manager of the Janus Henderson Global Unconstrained Bond Fund, said on Bloomberg Radio on Friday.

“And (he has to) tread carefully because it’s a changing number and it’s a new world in terms of credit.” On Thursday, President Trump said he will nominate Powell as chairman.

“It used to be, in nominal terms, around 4 percent and now, perhaps with inflation at 1.5 percent, it’s probably around 2. But that’s a probably. Nobody knows,” Gross said.

Trump will likely appoint dovish nominees to the central bank in the future and probably has four more appointments if Fed Chair Janet Yellen resigns, as expected, Gross said.

“I presume that they’ll be doves,” he said. Either way, “I hope he appoints someone with a more subjective as opposed to model-driven view.”