In all of the graphs we show bars of statistical errors assuming a perfect binomial distribution.
For example, in the graph of Use V. Month of Visit, during the month of March, 618 visits were made and the oven was in use in 368 of those visits.
Total number of visits: N = 618
Probability of Use: P = 368/618 = 0.60 (o 60%)
Standard Deviation: s = Ö ( P * (1-P) / N ) = .02
What is seen in the graph is 100 * (P ± s) o 60 ± 2 %