Hello, In Accounting & Finance module -->Journal Entries-->Journal voucher--> Create Now 4th field from top to bottom is REF#

I want it to be auto generated initially it appears as an empty field and i think it's a non processing field too like if I leave it blank it would be alright but still for my record maintenance I want to Make It AUTO GENERATED:

Like first voucher created REF#1 Second Vocher Created REF#2 Another Thing when I create my first voucher with my partner ABCD.I want it to be serialized like if I click create once again my Partner Field should be Filled with ABCD. and so on.Kindly Help me in it Thanks in advance.