code: def storeMasters(self, master_values, *, round=round):
      deltas = self._model.getDeltas(master_values, round=round)
      base = deltas.pop(0)
      return base, self.storeDeltas(deltas, round=noRound)
  
imports: from fontTools.misc.roundTools import noRound, otRound
  from fontTools.misc.intTools import bit_count
  from fontTools.ttLib.tables import otTables
  from fontTools.varLib.models import supportScalar
  from fontTools.varLib.builder import buildVarRegionList, buildVarStore, buildVarRegion, buildVarData
  from functools import partial
  from collections import defaultdict
  from heapq import heappush, heappop
label_desc: Use image node_id 6 for calling the OnlineVarStoreBuilder obj's underlying member method code with example usage: obj.storeMasters(master_values) and returns: base,  self