calculation of shift depreciation for 2 shift

Hi All

We have a one machinery running in three shift, dep key Streight line method i.e dep 10.34% for three shift accordingly we have maintain useful life

but now that machinery is working in Two shift for next two month , how i can calculate the Dep. for two shift?

Can i change the useful life according to dep % for two shift? pl guide me

Thanks in advance

Regards

Vishvas B