Where the value of n is a number, indicating the sample content. SD value is standard deviation, which is a statistic describing the discrete distribution of a group of variables. The value of m is average, arithmetic average.

Three-line tables usually have only three rows, namely, top row, bottom row and column row. The upper and lower lines are thick lines and the column lines are thin lines. Of course, a three-line meter doesn't necessarily have only three lines, and auxiliary lines can be added when necessary, but no matter how many auxiliary lines are added, it is still called a three-line meter. The elements of three-line table include: preface, title, item column, text and comments.