Writing the overall cell reaction for the Calomel electrode
The calomel electrode is not a cell. It can be part of a cell. It is a half-cell. A cell is made of two electrodes, one calomel electrode and another one. The reaction occurring in the calomel electrode is the reaction you present as &quot;overall cell reaction&quot;. What you described as &quot;anode half-cell&quot; has nothing to do with electrochemistry. It is the equation describing how $\ce{Hg_2Cl_2}$ gets dissolved in water.