Absolute energy calibration and the use of timing information of the BESIII EMC

We introduce the absolute energy calibration of the electromagnetic calorimeter at BESIII. The precision after calibration is about 0.5% and the resolution difference between data and the simulation is about 5%. We also present a method to veto beam-gas background using the timing information of the EMC, which is crucial for physics analyses involving low energy photons at BESIII.