Source: shrIkaraH
One may perform a minimum of 4 lakhs of Japa and then perform dashamsha homa with Payasanna.
The other method for Purashcharana is to start the Japa from the Agni Tithi (Pratipat) of Ashwayuja and chant 9 lakhs of the mantra till Ashtami. This is done in the Shukla Paksha of the month.
On the Navami day, dashamsha Homa (adding Swaha at the end of the mantra), dashamsha Tarpana (adding ‘Chandika Tripyatu’ at the end of the mantra) and Dashamsha Brahmana Bhojana are to be done.
(90k Ahuti-s, 9k tarpaNas and 900 bhojana-s on navamI? how’s that practical??)
By this, one obtains the Siddhi of the mantra and grace of Sri Chandika Parameshwari.