doubling time Math - title in biotechnology

https://dx.doi.org/10.1351/goldbook.D01855
The time (Math - text, Math - text) required for a cell population to double either the number of cells or the active cell mass.
Source:
PAC, 1992, 64, 143 (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 152