"primary guide" is correct and usable in written English.
You can use it to refer to a person who provides instruction or guidance in a particular area, such as a "primary guide to the study of history."
In the 20th century, Canopus is one of the primary guide stars used to navigate spacecraft.
"While the other world religions emphasized mystery and intuition," Stark writes, "Christianity alone embraced reason and logic as the primary guide to religious truth".
Sharpe's novel rotates the point of view among members of a Connecticut family; our primary guide is Chris, a bitterly intelligent boy rolling bored through high school.
"We are conscious this is a sensitive time, but our primary guide is what is needed for Taiwan's security," said Undersecretary of Defense Walter B. Slocombe.
Over the past year and a half I have become more reliant on what you call the metrics, but that has never been a primary guide for me.
Sharpe's second novel rotates the point of view among the members of the Schwartz family of Connecticut; of these, our primary guide is Chris, a bitterly intelligent boy rolling bored through high school.
Our primary guides are Jon Roberts and Mickey Munday, twin pillars of the low-life population, complete with disco hair, criminal records and colorful tales of their exploits with the Medellín cartel.
Given the limited predictive success and the lack of consensus in social sciences, their conclusions can seldom be primary guides to setting policy.
The primary guides are often family men, and while I'm not a relative, they tend to treat me like one, acting like a father, brother, or uncle for brief portions of the trip.
Most, if not all law, students are either assigned The Bluebook or the ALWD Guide to Legal Citation as the primary guides to legal citation, which brings into question how Introduction to Basic Legal Citation stands out.
In turn, this court, consistent with legislative policy, has pointed to the "will of the voters" as the primary guiding principle to be utilized by trial courts in resolving election contests: "The real parties in interest here, not in the legal sense but in realistic terms, are the voters.
