Chemotaxis assays are experimental tools for evaluation of chemotactic ability of prokaryotic or eukaryotic cells.
A wide variety of techniques are known and applied for such reason. Some of them qualitative and investigator can determine whether the cells prefer or not the tested chemical, others are quantitative

Quantitative property

A quantitative property is one that exists in a range of magnitudes, and can therefore be measured with a number. Measurements of any particular quantitative property are expressed as a specific quantity, referred to as a unit, multiplied by a number. Examples of physical quantities are distance,...

 and we can get information about the intensity of the responses in a more detailed way.
In general, the most important requisite to calibrate the incubation time of the assay both to the model cell and the ligand to be evaluated.