Karmandir 
About
The Shukra Yantra is the number yantra of Shukra dev, also known as Shukracharya, the guru of the daityas. Its nine numbers run from 6 to 14, the Surya square with 5 added to each, so every row, every column and both diagonals add up to 30, with 10 in the middle. In the full Navagraha Yantra, Shukra's square sits on the east side, the place the Matsya Purana gives him. Families keep it in the puja place and remember Shukra dev on Fridays with his verse from the Navagraha Stotram, which calls him white as snow and a teacher of all the shastras.
Parts of the yantra
Number square: nine cells, written in Devanagari digits in the drawing — top row 11, 6, 13; middle row 12, 10, 8; bottom row 7, 14, 9. Every row, column and diagonal totals 30, and 10 sits in the middle cell. Any two numbers facing each other across the middle always add up to 20. Lines: a gold outer line closes the square and saffron lines divide it into nine cells. Frame: a plain border of three lines around the square, marking the yantra's space.
How to use it
Place the yantra upright on a clean cloth in the puja place. On a Friday, or on any day, light a diya, offer a flower and sit quietly facing it. Rest your eyes first on the middle number, 10, then move them through the numbers from 6 up to 14, one cell at a time; this gives the mind one calm thing to follow. Then read Shukra dev's verse from the Navagraha Stotram (हिमकुन्दमृणालाभं…) once, or 11 times. Wipe the yantra with a soft, dry cloth to keep it clean.
हिमकुन्दमृणालाभं दैत्यानां परमं गुरुम्। सर्वशास्त्रप्रवक्तारं भार्गवं प्रणमाम्यहम्॥
Himakunda Mrinalabham Daityanam Paramam Gurum. →
Frames differ from print to print: the NCERT figure, for example, draws this square inside a six-pointed star. Many prints use the digits 1, 2, 3 instead of the Devanagari digits used here. The numbers and their places stay the same.
