dizzy base tells the ecu what the mechanical motor timing is via the TDC & CKP sensors in the base.CYP sensor just tells the ecu which cylinder needs attention by indicating No1 cylinder.
base timing is having the ecu & motor agree on what is happening.
u short the diagnostic plug to remove any compensations the ecu might be making to the timing due to temperature/elec load/etc,& ecu will hold the timing at a fixed value,eg 16deg on a Bseries,& then u can go match the mechanical timing at the motor,by making the TDC & CKP sensors in the base agree with the timing mark on the crank pulley.
ecu cant correct anything if it doesnt know whats actually going on to begin with.