• Ashley, Mike (2007). Gateways to Forever: The Story of the Science-Fiction Magazines from 1970 to 1980. Liverpool: Liverpool University Press. pp. 479-481. ISBN 978-1-84631-003-4.
• Ashley, Mike (2016). Science Fiction Rebels: The Story of the Science-Fiction Magazines from 1981 to 1990. Liverpool: Liverpool University Press. pp. 440-442. ISBN 978-1-78138-260-8.
• Ashley, Mike (2022). The Rise of the Cyberzines: The Story of the Science-Fiction Magazines from 1991 to 2020. Liverpool: Liverpool University Press. pp. 409-11. ISBN 978-1-80085-648-6.

Notes:

• Ashley's data comes from two sources: the annual statement of circulation published in the magazine, and additional data provided to Locus magazine each year starting in 2004.
• The data runs approximately from summer of one year through summer of the next year, so two year dates are given for each data point.
• No data is available for 1979-1980.
• Digital subscription numbers for the first few years are estimated.