My lucky day! A box of HP Application Notes arrived from the USA, and it turns out one of them had a HP slide calculator I hadn't seen before, clipped to it. From 1965, still in the original envelope and in perfect condition. Just camera shots below, not scans as I'm short of desk space atm.
Btw, about scanning and PNG file size... a few hints.
1. Preprocess the images (in full hi-res RGB mode), to remove blemishes. If the paper is supposed to be a uniform color (white or whatever), make sure that the 'blank' areas in the image are actually all that exact color. The RLL compression used in PNG is useless if the background is a noisy mess. Ditto for inks - the only shading should be on the edges of inked areas. And anything 'screen printed' (an array of tiny dots) has to be converted to the actual solid color (or shading) that was the printer's intent for your eye to see. When adjusting color ranges, don't overdo it, as you'll make line & font edges look jaggy. Preserve enough luminance scale!
2. Once you've got the image looking like it was supposed to look (before print screening, dirt, paper aging, etc) messed it up, then you can optimize the final image resolution and file encoding. Scale it to the smallest size that fully preserves the finest visual detail.
Then convert it to a decent format like PNG, using a utility that allows you to adjust parameters like how many bits per pixel. If the image is B&W text, then grayscale 4 bits/pixel is adequate, since font edge shading with 16 gray levels works fine. Posterized color images with few colors can also sometimes work with 4 bits/px. Or go to 8 bits, for 256 colors. For ful color images, full palette.
One of the main strengths of PNG is its flexibility. But this advantage is lost if you don't know how to use it, or your software tools don't allow it.
In Irfanview, the 'export for web' facility lets you adjust compression factors like that and see the anticipated final file size on the fly, before actually outputting the file.
With both image background 'noise' cleanup, and final image compression mode optimization, you'll be amazed at what small filesizes can still contain hi-res clean images.
Meanwhile, three crummy JPG images below...