186101 (HS2161) Technical English I Lecture Notes Graphs

“A picture is worth a thousand words”. Graphs or charts help people understand data quickly. Whether you want to make a comparison, show a relationship, or highlight a trend, they hel[p to transfer the information quickly. There are different typesw of graphs and charts like Flowchart,Piechart, Bargraph, and so on. To create most charts or graphs, excluding piecharts, you typicaqlly use data that is plotted in two dimensions. The horizontal dimension is the y-axis

Bargraphs show relationships between different data series in the spaced bars horizontally or vertically. Here the height of the bar represents the measured value or frequency. The higher or longer the bar, the greater the value. Legends are used to list the variables appearing in the chart and an example of their appearance. This information allows the data from each variable to be identified in the chart.

The following table lists the number of seats allocated to each party group in European elections in 1999 and 2004. The results of 1999 have been multiplied by 1.16933, to compensate for the change in number of seats between those years.
This bar chart shows both the results of 2004, and those of 1999:

 A piechart compares parts to a whole . as such it shows a percentage distribution . the entire pie represents the total data set and each segment of the pie is a particular category within the whole. So, the piechart is used for measuring the data , which depicts a ratio or percentage relationship.


A pie chart for the example data.
An exploded pie chart for the example data, with the largest party group exploded.
The following example chart is based on preliminary results of the election for the European Parliament in 2004. The table lists the number of seats allocated to each party group, along with the derived percentage of the total that they each make up. The values in the last column, the derived central angle of each sector, is found by multiplying the percentage by 360°.
Percent (%)
Central angle (°)

*Because of rounding, these totals do not add up to 100 and 360.

The size of each central angle is proportional to the size of the corresponding quantity, here the number of seats. Since the sum of the central angles has to be 360°, the central angle for a quantity that is a fraction Q of the total is 360Q degrees. In the example, the central angle for the largest group (European People's Party (EPP)) is 135.7° because 0.377 times 360, rounded to one decimal place(s), equals 135.7.

Flowcharts are helpful in understanding a complicated process . this is especially true if you have to make decisions and do different steps depending on those decisions. By looking at a flowchart you canvisually follow different paths through the chart . here are some guidelines to draw a flowchart.
                All  flowcharts starts and end with the terminator or terminal shape like a rounded rectangle.
To show the flow arrow mark is used.
Decision shape is used to ask a questions.
The rectangle is used for activities or action steps that must be done.
A circle containing a letter or number is used to show that it is connected to another chart on a different page.

Flowchart building blocks


A simple flowchart for computing factorial N (N!)
A flowchart for computing factorial N (N!) where N! = (1 * 2 * 3 * ... * N), see image. This flowchart represents a "loop and a half" — a situation discussed in introductory programming textbooks that requires either a duplication of a component (to be both inside and outside the loop) or the component to be put inside a branch in the loop. (Note: Some textbooks recommend against this "loop and a half" since it is considered bad structure, instead a 'priming read' should be used and the loop should return back to the original question and not above it.[7])


A typical flowchart from older Computer Science textbooks may have the following kinds of symbols:
Start and end symbols
Represented as circles, ovals or rounded rectangles, usually containing the word "Start" or "End", or another phrase signaling the start or end of a process, such as "submit enquiry" or "receive product".
Showing what's called "flow of control" in computer science. An arrow coming from one symbol and ending at another symbol represents that control passes to the symbol the arrow points to.
Processing steps
Represented as rectangles. Examples: "Add 1 to X"; "replace identified part"; "save changes" or similar.
Represented as a parallelogram. Examples: Get X from the user; display X.
Conditional or decision
Represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test. This symbol is unique in that it has two arrows coming out of it, usually from the bottom point and right point, one corresponding to Yes or True, and one corresponding to No or False. The arrows should always be labeled. More than two arrows can be used, but this is normally a clear indicator that a complex decision is being taken, in which case it may need to be broken-down further, or replaced with the "pre-defined process" symbol.
A number of other symbols that have less universal currency, such as:
  • Document represented as a rectangle with a wavy base;
  • Manual input represented by parallelogram, with the top irregularly sloping up from left to right. An example would be to signify data-entry from a form;
  • Manual operation represented by a trapezoid with the longest parallel side at the top, to represent an operation or adjustment to process that can only be made manually.
  • Data File represented by a cylinder.
Flowcharts may contain other symbols, such as connectors, usually represented as circles, to represent converging paths in the flowchart. Circles will have more than one arrow coming into them but only one going out. Some flowcharts may just have an arrow point to another arrow instead. These are useful to represent aniterative process (what in Computer Science is called a loop). A loop may, for example, consist of a connector where control first enters, processing steps, a conditional with one arrow exiting the loop, and one going back to the connector. Off-page connectors are often used to signify a connection to a (part of another) process held on another sheet or screen. It is important to remember to keep these connections logical in order. All processes should flow from top to bottom and left to right.


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