The method described in the patent deals with taking samples of perspiration of the individual by measuring one or more electrical properties of sweat with the help of electrodes in the watch. The data gathered in the form of electrical properties could then be correlated with the concentration of electrolytes present in the sweat. As mentioned, some electrodes present at the base of the Apple Watch dial, positioned on the inner side of the wrist strap, could do the trick of data collection by measuring the electrical properties.
As per the report, “a high level of electrical conductance of the perspiration can indicate a high concentration of electrolytes and a low level of hydration” and vice versa. These measurements can then be used to alert the user and give feedback as to the hydration levels in the body while he/she is engaged in some fitness-related activity.
The figure included in the report outlines how the process is going to work. In the figure, an Apple Watch band (#110) is shown with the electrodes (#140) positioned within cavities (#160) formed in the support structure (#120).
The report says: “The cavities can each be recessed within the support structure to form a space for receiving perspiration. This can be accomplished, for example, by capillary action to facilitate measurement of the perspiration without requiring the electrodes to be positioned on an outermost surface of the Apple Watch band. The cavity further provides known dimensions (e.g., height, width, length, volume) for a sample of perspiration. These known dimensions can be used to calculate electrical properties based on given measurements. Each cavity can contain one or more electrodes. Multiple cavities can be interconnected by channels, for example forming a mesh or network of cavities in fluid communication with each other.”