Tantric yantras are precise geometric forms that have been used for centuries as tools for self-realization and the attainment of mystical powers. In Tools for Tantra , Tantric practitioner and scholar Harish Johari has re-created the exact colors and proportions of the primordial yantras along with step-by-step instructions for their accurate construction, coloring, and use.
This is a great guide for creating yantras and using them for meditation. It is also a great introduction to Tantra, the use of mantra, and the goddesses (and yantras associated with them) of the Mahavidyas.