Previously, I purchased few Yantras of Gods and Goddesses and kept in my Puja room. Even after 20-30 years, these yantras are still there and I worship them. I have not noticed any positive change in my life though.
Recently, I read a lot about Yantra and came to know that these sacred geometries are machines. A yantra needs regular meditation on it's bindu to make it work.
Few pandits say that these require Pran Pratistha. Now the question is how to know that pandit was successfully able to do Pran Pratistha.
How to make a Yantra work? After how many days I can expect any positive result, howsoever small?