subtract from previous row

Hi Friends...Need your help in creating measure that subtract value from previous row and it has to re-start with the same logic when the next quarter starts. Please find the attached screenshot for your reference. I already have a measure called “X”. I need your help to create X1 measure that subtract value of X from previous row. Example, please find the attached the excel (C and D column). 1 quarter contains 13 weeks. Kindly do the needful.