Detectives Position

Can someone tell me how you promote to detetive in SJPD? Do you take a test? Do you interview for openings? Do you rotate from detective back to patrol? Do you only use Sargeants as Detetives?? SFPD is about to consolidate the rank of Inspector (Detective) with Sargeants. All Inspectors will now become Sargeants and all Sargeants are now able to work as Inspectors (Before that had to take the Inspectors test to become dual rank Sargeant/Inspector). Is this how you do it??

Thanks