Extremely RARE Hewlett Packard HP-28S Clear Case Vintage Calculator

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Extremely RARE Hewlett Packard HP-28S Clear Case Vintage Calculator:
$1888.30

Selling an extremely rare Hewlett Packard clear cased 28S calculator. This is from my personal collection that I am downsizing - this item is one of my prized clear cased HP calculators. My clear cased and prototype HP\'s can be viewed far as I know, HP used clear cases for two reasons: 1. to view how well the electronics fitted inside the casing (before the days of 3D CAD); and 2. as a marketing tool when sales reps would show HP\'s latest products and how advanced they were. There is no serial number on the case of this HP28S, so it\'s likely to be a marketing product, or it\'s a very early test pre-production prototype of the shell.
It passes all self tests and works perfectly. The battery door (which is also clear plastic) is in perfect condition. There is a small hairline crack in the case where the battery door connects - this was a common problem in the 28S. Note also that the alpha keys differ from the normal production model.
Comes with an original black vinyl case. Batteries not included (takes 3xN cells).
Because of its rarity, I have listed quite high - I will consider all reasonable offers, but if it doesn\'t sell then I will be returning to my collection and I won\'t be re-listing it.
I will ship worldwide with tracking and insurance.