Transaction quanity and primary quantity differnce?

hello experts,

while doing OPM Reconciliton,

when i finding output of -

select sum(transaction_quantity), sum(primary_quantity)  from mtl_material_transactions where inventory_item_id = 8

and organization_id in (86) and transaction_date >=  TO_DATE('31-Dec-2009 00:00:00','dd-mon-yyyy hh24:mi:ss')

and transaction_date <=  TO_DATE('30-apr-2013 23:59:59','dd-mon-yyyy hh24:mi:ss')

it gives ->

SUM(transaction qty) = -13893227.775

SUM(primary qty)  =  42423

can Transaction qty and primary qty must be same???

in my case ,why this happens???

waiting for valuable update

Kunal.