San Francisco Board of Supervisors President David Chiu, who became The City’s acting mayor after Gavin Newsom’s swearing-in as lieutenant governor on Monday, has taken a “low-key approach” to his brief stint as The City’s most powerful politician.

The Board of Supervisors is expected to approve City Administrator Ed Lee as interim mayor later Tuesday.

Until then, under the city charter, the president of the Board of Supervisors is acting mayor.

Chiu became mayor at 1:24 p.m. Monday, but is taking “a decidedly low-key approach” to his new and temporary powers, his chief legislative aide Judson True said.

“He brought his lunch and ate it at his desk,” True said.

He said Chiu has not used his mayoral powers to do anything other than attend meetings and touch base with various city officials.

On Monday, under his authority as board president, Chiu worked on assigning supervisors to the board’s various committees, True said. He will announce the assignments later Tuesday.

Lee is expected to be sworn in as interim mayor later Tuesday afternoon after the board meeting. He will serve about a year in office, and is not expected to run for mayor in the next election in November.