It's widely known that saliva changes its properties as various chemical and biological processes take place in the female organism, including ovulation. It's also a long-known scientific fact that there are biochemicals concentrations of which in the female body are linked to the presence of ovulation, with lutropin (also known as luteinizing hormone, or LH for short) being the most important of all. Lutropin is produced in the anterior pituitary gland and one of its few functions is to trigger ovulation directly.

Conventional non-laboratory methods of measuring salivary LH level have proven to be too imprecise to be relied upon when trying to detect ovulation. In order to measure the level of LH, a chemical needed to be found concentration of which in saliva has a very strong correlation with that of LH, and it should be possible to measure the level of this chemical in saliva at home with great precision.

After long clinical research (in which about 10,000 female participants took part) it was found that from all the chemicals present in saliva (which together make up only about 2.5% of saliva contents, with the rest being pure water, H₂O), only the level of potassium (chemical element K) bears an enormously strong correlation with the level of LH (research done by another team of scientists and doctors independently confirmed this in 2010, here is the paper). It was no surprise that the long-sought chemical turned out to be potassium, because potassium has long been thought of in medicine as a trustworthy indicator of major changes in the human organism. So finally, it was salivary potassium level that we decided Vesta should measure.

Out of all possible ways to measure this level, it was found that the most precise method to date takes advantage of a technique called polarography, invented by a Czech chemist Jaroslav Heyrovský, for which the Nobel prize has been awarded to him. Taking into consideration the peculiarities of polarography, the right shape for the sensor of Vesta, the material from which its electrodes should be made of, the way to process and parse information the sensor receives, etc., were chosen in order to achieve a maximum sensitivity to the chemical of interest.