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Mechanical pencils are also old invention dating even from 16th century. First ones were relatively simple mechanisms, only to become more complicated with time. Today we have mechanical pencils which can write and draw very precisely.
Fountain pens replaced standard metal pens because they were easier to use and were less messy. After years of improvements (and after appearance of ballpoint pens which are even easier to use) they became a sort of status symbol. Read more about history of fountain pen.
Beginning of use of pen and ink marked the start of new era of easier recording of information. Without them, early scientific discoveries would be forgotten and development of humanity would be much slower.
Pencil practically cannot be used without some kind of pencil sharpener. Were they simple knives or complex machines with many rotating elements, their purpose is to make a fine point to a pencil. Read more about pencil sharpener history, facts and types.