Question about notation used in a schematic for ADM-3A

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stragulus

Joined Feb 9, 2016
12
Hi, I've been debugging an ADM-3A serial terminal for a while. When studying the schematics, I found some notations that I do not know what they represent. As an example, please see this image here that I cropped from the maintenance manual:

adm-3a schematics sample.png

What does the 280 here represent? It doesn't seem like a standard notation. Nor can't I figure out from the context what it means. Maybe it's just something internal to the manufacturer, but maybe it's a hint that I'm missing. Anyone knows?
 
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