Starting with Cycle Day 2, a woman uses the oral sensor to take an oral reading each morning, just after waking, and before eating or drinking. The monitor will track trends in the oral readings, and will be looking specifically for a trend called the Cue Peak. The Cue Peak, or the peak value in salivary electrical resistance (SER), is a high oral reading followed by two lower oral readings. This Cue Peak trend reflects hormonal changes that coincide with the selection of the dominant follicle. Once the dominant follicle is selected and begins to mature, increased estrogen production causes an increase in adrenocorticotropic hormone (ACTH) and aldosterone, which causes an increased production of sodium chloride (NaCl). This increase in NaCl is reflected in the saliva. The peak SER reflects the lowest levels in NaCl production, and occurs simultaneously with the selection of the dominant follicle. Because the selection of the dominant follicle occurs 5-7 days before ovulation, once the monitor detects the Cue Peak trend it is able to predict peak fertility up to 7 days in advance. The monitor displays a fertile window on the calendar in varying shades of blue, with the darkest blue indicating peak fertility. To maximize the chances of conceiving, women should time intercourse daily on the darkest blue days, and every other day on the light blue days.