Tapestry/Method of calculating base stitches and adjusting them according to the pattern (Part 7)

A detailed explanation of how to calculate the number of stitches in the base along with the number of the pattern 👇🏽
★How can we adjust the number of stitches in the base with the number of the pattern and at the same time adjust the appropriate and required size?
★ How can we change the size and the number and also fit the pattern?