Do you often find that you have 'good' days and 'bad' days? Some days, you will be fill of confidence, while at other times, you will be unable to do anything right. Wouldn't it be useful if you could some how predict which of those days would be when? You would be able to plan your life much more easily. Biorhythms are such a way of predicting these good and bad days. Everybody has three cycles, or biorhythms, which each alternate between positive, or high (denoted by H), and negative, or low (L) phases. They are the Physical, Sensitivity (or Emotional) and Intellect cycles. Each cycle begins the day we are born, and takes a set amount of time to complete; 23 days for the physical, 28 days for the sensitivity, and 33 days for the intellect. Therefore, to calculate what stage each cycle will be in on a particular day, the number of days since you were born must be calculated.