Count the number of characters in each alphabet you wish to compare. Record the number of different ways you can write each character. For example, in the Roman alphabet the letter "A" can appear five different ways. It can be printed as a capital and a lowercase as well as written in cursive as a capital at the beginning of a word and a lowercase at the beginning, middle or end of a word. Write down any other metrics by which you wish to compare alphabets.
Draw XY axes on a piece of grid paper. Label the X axis "Alphabet" and write the names of the alphabets you are comparing. Write the measurement with which you are comparing the alphabets along the side of the Y axis. For example, write "Number of Letters" if you are comparing alphabets by the number of letters.
Scale the Y axis with the numbers for the quantitative metrics you selected above. For example, if you are comparing the number of characters in several alphabets that range from 18 to 32 characters then you may increase each interval by twos.
Draw a bar above the name of the alphabet indicating the value for the metrics being compared. For example, if you are comparing the number of letters in alphabets then you would draw a bar above the Phoenician alphabet that rises to the 22 mark on the Y axis to indicate that it has 22 letters.
Color-code the bars if you are comparing multiple metrics. For example, if you are comparing alphabets by the number of characters and the number of sounds then you would color one bar green and the other blue to indicate which bar represents which metric.