The phrase "an indication of the quantity" is correct and usable in written English.
It can be used when referring to a measurement or signal that represents how much of something there is.
Example: "The scale provides an indication of the quantity of ingredients needed for the recipe."
Alternatives: "a measure of the amount" or "a sign of the volume".
The results of this assay provide an indication of the quantity of the peripheral arm of Complex I in preparations of membrane vesicles, and so is complementary to immunoblots of the membrane subunits.
The turbidity of culture solution was measured in a Microplate Spectrophotometer (Benchmark Plus, BioRad, CA, USA) at λ = 590 nm at 30 min intervals, providing an indication of the quantity of yeast cells (Blomberg, 2011).
Before setting out how a study of this nature might be achieved, two systematic reviews are presented, one on population-based descriptive epidemiology and one on cognitive outcomes after delirium in prospective studies, which together provide an indication of the quantity and quality of previous work in this field.
It is useful at this point to give an indication of the quantities and variety of crop residues available in East Africa.
Although this experiment demonstrated that single primary electrons could be detected the chip did not provide information on the arrival time of the electron in the sensitive gas volume nor did it give any indication of the quantity of charge detected.
Asphyxiated neonates displayed higher glycine concentrations and percentage glycine of the sum of l-serine and glycine (an indication for the amount of glycine synthesis from l-serine) and in the most serious case of asphyxia also lower d-serine concentrations and percentage d-serine of the sum of d- and l-serine (an indication for the quantity of d-serine synthesis from l-serine) than controls.
More generally speaking, the identification of certain algal taxa and their quantities gives an indication of the water quality of river basins and bathing water.
"This quantity of muons, the muon flux, gives you an indication of the average density of matter in that direction".
The primary advantage of using genes expressed within the cells investigated as reference genes is that they also function as endogenous controls, since they are exposed to the same conditions in vivo and in vitro, thereby providing a direct indication of the quantity and quality of the samples.
