Myth behind Durga being worshipped as Chamunda___________
While the Goddess and Mahishasura were engaged in a fierce battle, the two generals of Mahisha, Chando and Mundo attacked the Devi from the the rear. Durga appeared to them, a brilliantly glowing woman with her hair knotted on her head, a crescent moon above her forehead, a 'tilak' on her forehead and a garland around her neck. With golden earrings and clad in a yellow saari she emitted a golden glow. Her ten hands possessed ten different weapons. Though she appeared beautiful her face turned blue with anger when she faced Chondo and Mundo. From her third eye then emerged a Devi with a large falchion and a shield. She had a large face, bloody tongue and sunken blood shot eyes. She was Chamunda. With a bloodcurdling shriek she leapt forward and killed them. This moment was the juncture of the 8th and 9th lunar day. 

Age old yardsticks for measuring the "Sandhikhan"____________
Long back devotees in order  to perform the Sandhi Puja at the exact juncture used a number of methods. With the last 24 mins. of the Ashtami puja still left, a bronze bowl with a tiny hole was placed in a bucket full of water. The bowl  with the tiny hole was made in such a way that it took exactly 24 minutes for the bowl to submerge in the water. The moment the bowl submerged in the water cannon balls were

fired announcing this moment of Sandhi Puja. This yardstick for measuring the "Sandhikhan" was very popular ages ago in many "Rajbaris". Many "Rajbaris", including, the zamindar of Sutanuti of Sobhabajar Rajbari  fired cannon balls to announce the "Sandhikhan". People around Sobhabajar waited for this indication to proceed with their puja. King of Krishnanagar, Raja Krishna Chandra, was given the cannon of Plassey as a gift from Robert Clive. In Shikharbhum Rajbari a platter with vermillion (sindur) used to be kept in front of the Devi.

It is said the foot prints of the Devi could be seen in the platter. This moment indicated the commencement of Sandhi Puja. Sabarno Raychoudhury of Barisha worshipped the Chamunda Devi by burning 'Layta' and 'Pholui' (types of fishes) fishes.  

Things needed to perform Sandhi Puja_____________________
Sandhi Puja requires 108 lotus flowers, a single fruit, dry rice grain for "noibiddo", 108 earthen lamps, clothes, jewelry, hibiscus garlands and wood apple (bel) leaves. The almost non existent rituals which underwent changes with the changes in the society can still be seen in some of the 200-250 year old Pujas.