As Clark County’s governing body convened for the first time in 2015 on Tuesday, it didn’t take long for county Councilor Tom Mielke to recognize the significance of an otherwise routine meeting.“Tonight we’re going to make history,” Mielke said.Tuesday marked the first official meeting for the group as the Board of County Councilors, which assumed new roles and titles as a result of a home-rule charter voters approved in November. The three served as county commissioners until Jan. 1, when the new form of government began to take effect.That’s not the only change. Two additional councilors will be elected this year to complete the transition from three commissioners to five councilors. County Administrator Mark McCauley also became acting county manager, a position that carries new power under the charter. The manager has executive authority over county departments, while the council sets policy. Previously, county commissioners held both executive and legislative powers.The council on Tuesday picked Councilor David Madore as its chair for this year, following the regular rotation the county has used. But that’s the last time the group will choose its own chair — later this year, voters will directly elect a county chair that will serve beginning in 2016.The council discussed the transition in response to a few public comments during the meeting. Madore addressed a proposed “charter implementation process agreement,” which he first floated at a meeting last month.