The tidydata contains 180 observations and 68 variables where 66 are the features and other two are subject id and activity name respectively. The 180 = 3*60 observations are for 6 activities for each of the 30 subjects. The 66 variables are the average value of that particular measurement for that particular subject and activity. Out of the 66 variables, 33 variables are those with mean appended to their names in features.txt and other 33 are those with std appended to their names.