Following steps are taken.
(a) Add mid values of two successive classes.
(b) Divide it by 2.
(c) It is upper limit of preceding class and lower limit of successive class.
(d) Find the difference between mid values of two successive classes.
(e) Deduct it from the upper limit obtained to get lower limits of the preceding class.
(f) Repeat it for all classes if classes are unequal (if difference between different mid values is different) and if classes are equal (if difference between different mid values is equal) simply keep on adding the difference between two successive mid values to find the upper limits of different classes.

General rules to construct a Time Series graph
(a) Since time can never be in negative values, II and III quadrant are not used in making of time series graphs.
(b) Time period (week, Month, Year) is taken on X- Axis. And Variable under study is taken on Y-Axis.
(c) We start Yaxis with Zero and decide the scales for both the axis.
(d) Different values are plotted on the graph.
(e) By joining these points, we get a time series graph.
Time series graph can be of three types:
(a) One Variable Graph
(b) Two or more than two variable Graph
(c) When False Base Line is used
(d) Graphs of Different Units

When information is presented over a period of time, it is called time series graph. In it, time (hour, day/date, week, month, year, etc.) is plotted along x-axis and the value of the variable (time series data) along y-axis. A line graph by joining these plotted points, thus, obtained is called arithmetic line graph (time series graph). It helps in understanding the trend, periodicity, etc. in a long term time series data. An example is given below:

Variable is shown on X axis and frequencies are shown on Y axis.

When class intervals are unequal, we follow the steps given below:
(a) Take the class which has the lowest class interval.
(b) Do not adjust the frequencies of the lowest class.
(c) Frequencies of other classes are adjusted according to the lowest class interval.
(d) Formula for adjusting frequency is:
\(\frac { Frequencyofthegivenclass\times Lowestclassinterval }{ ClassIntervalofgivenclass } \)
(e) Keep the width of the rectangle according to class interval of the concerned class and length of the rectangle according to the adjusted frequency.

A frequency polygon can also be converted back into a histogram by drawing vertical lines from the bounds of the classes shown on the horizontal axis, and then connecting them with horizontal lines at the hieghts of the polygon at each mid-point. Frequency Polygon can be drawn in two ways:
Method:
(i) Draw a suitable Histogram as explain in the previous section following all the basic principles.
(ii) Get the mid points of the upper horizontal side of each rectangle.
(iii) Join these mid points of the adjacent rectangles of the histogram by straight lines.
(iv) Ends of the frequency polygon are to be extended to mid point of classes at both sides.
(v) Labelling should be properly done and scale of measurement should be clearly shown.
An example is shown below

Usually, when we draw any graph, the scale on which the graph is measured starts from zero on the y-axis. However, under the situations when the data to be plotted on graph starts from a value which is far above zero, results in the problem of shortage of space on graph. To overcome this problem of shortage of space, a false base line is plotted. False base line is a line which is drawn to grasp the attention of the reader on the fluctuations which usually remains unnoticed.
A kinked line is used on x axis for the same purpose for which false base line is used for y axis. It means when variable starts from a higher value, we use kinked line and when frequency starts with a first higher number followed by smaller gaps, we use false base line.

Table showing distribution of production in two fortnights amongst internal consumption, exports and stock. (in tones)

In case of equal class interval simply we draw the frequencies of equal width but when class intervals are unequal these frequencies need to be adjusted. It will be clear from the example given below:

Depending on the number of variables involved, we determine whether we should use one way, two way, three way or multifold table. To present non workers in urban areas, we will use two way table.

(a) Simple bar Diagram
(b) Pie Chart
(c) Pie Chart

Method 1: Now it needs to be converted into exclusive series for constructing a frequency polygon.

When class intervals are unequal, we follow the steps given below:
(a) Take the class which has the lowest class interval.
(b) Do not adjust the frequencies of the lowest class.
(c) Frequencies of other classes are adjusted according to the lowest class interval.
(d) Formula for adjusting frequency is:
\(\frac { FrequencyofthegivenclassxLowestclassinterval }{ ClassIntervalofgivenclass } \)
(e) Keep the width of the rectangle according to class interval of the concerned class and length of the rectangle according to the adjusted frequency.
Adjusted Frequencies are:

When Frequencies are given by Inclusive Method
It is to be noted that a histogram can be prepared only from exclusive series as there is no gap between rectangles in a histogram. Therefore, if data are given in the form of exclusive series, then it needs ot be converted into exclusive series.