Excess Depreciation

In case of excess deprecation arising due to revaluation of a PPE , such excess depreciation maybe transfer to retained earning from revaluation reserve (OCI Reserves) at the option of the company,.
1)Does this transfer can be made each year or only in year when revaluation is done.?
In case it can be done each year :
2) Can Company transfer choose to transfer some year and ignore in some other years?
3) What in case of further revaluation, does the company has to compare depreciation on carrying amount at the time of initial recognition to the fair value of further revaluation?(eg: If co, initially record it at 10, then revalue at 12 then after few years again revalue at 15, then should we compare depreciation on 10 and 15 or dep on 12 or 15.)

Please help me by answering the query, Thanks in advance.