Requirement:  When Updating a record column in delegated Table, corresponding other Column to be taken previous value from initial changed column.

I have a situation, 
I am updating a column(Current Value) in a table, corresponding column(old Value) in same table will be having old value of (Current Value). I used declare trigger to achieve it. But now what is happening is, While Updating different Column (Not Current Value)then also Old Value is updating. How to restrict this ? Did any one come across this requirement?
Please provide solution.