The phrase "an indispensable reference" is correct and usable in written English.
It can be used to describe a source of information that is essential or crucial for understanding a topic or completing a task.
Example: "For anyone studying the history of art, this book is an indispensable reference."
Alternatives: "a crucial resource" or "an essential guide".
It will be an indispensable reference for all students of monetary economics.
Dickinson: Selected Poems and Commentaries will be an indispensable reference work for students of Dickinson and readers of lyric poetry.
Economic, Social, and Cultural Rights: A Legal Resource Guide is an indispensable reference work for all those working in the field of international human rights law.
Subtly and persuasively argued, his book will become an indispensable reference point for all concerned with twentieth-century German history and thought.
From romanticism through postmodernism, the imagination has become an indispensable reference point for thinking about the self, culture, philosophy, and politics.
This is an indispensable reference in planning the best start with the longest duration for the sculpture going up in 2018.
This well-organized reference is an indispensable source of information for everyone who seeks to develop understanding of health systems and to learn about historical, political, and socioeconomic factors that influence health policies at the global, national, regional and local level.
With a comprehensive bibliography of over a thousand references, Nonsmooth Dynamics is an indispensable source of information on impact phenomena and rigid-body dynamics.
Engler's Syllabus der Pflanzennamen (1892; "Syllabus of Plant Names") is still a standard and indispensable reference book.
Georges Bank provides a basic and indispensable reference tool for anyone involved in studying the bank or in making decisions about its use.
In bringing the available information on this complex region together for the first time, Georges Bank provides a basic and indispensable reference tool for anyone involved in studying the bank or in making decisions about its use.
