The manga series Oh My Goddess was originally published from 1988 until 2014. I am only familiar with the early comics from this series, so the following might not apply to comics from the later years – but there was always exceptional detail on products and technology. Specific products and their features were often being mentioned or hinted at. A lot of this information was about cars, motorbikes, cameras, but you can also see calculators and mechanical pencils in this series, as seen in the examples below.
I am not sure if the pencil from page 39 is supposed to be the same as the one from page 71, but it’s a great close up drawing. The sleeve seems, proportionally, rather slim, though.
There were many different version of the Zebra Knock Pencil. Some versions of the M-1300 had the text “A most suitable pencil for desk work” printed on the side. As far as I can tell the Zebra Knock Pencil is not being sold anymore and Zebra has replaced this model with more high-end mechanical pencils.
The images have been taken from the English version of Oh My Goddess, published by Dark Horse Manga as Volume #5. I believe that the use of these images falls under “fair dealing” as described by the UK Copyright service.