[Jack]

A little more trivia: back in the 40's, etc, there were 2 types of scopes. The internal adjustment type, like all our scopes are today, and the external adjustment type. Back then, about the highest power you could get in an internal adjustment scope was 6x, and some makers didn't make anything more powerful than 4x.
If you wanted a high power scope, you got an external adjustment type, like the Litschert that Larry's described. Unertl was well known for making that type scope, too. Those type scopes could be had in 10x or more.
The external adjustment scopes were mounted on the barrel, with 2 brackets that held adjustment knobs. The brackets were often quite far apart. That set up did allow very repeatable and precise adjustment, at a time when repeatable and precise adjustments were far from universal, or even common.
The drawback to the external adjustment types were: they were bulky, and delicate. Also, they mounted on the barrel, which we know now is not the best thing for ultimate accuracy. That's not a new discovery - some shooters knew then that anything that interfered with barrel harmonics was not an aid to accuracy.
The internal adjustment scopes (like today's) mounted on the receiver, hence no problems with the barrel. But, not enough power for target and varmint shooters. Hence, Litschert's attachments - they were a way to get a receiver mounted scope with enough power to shoot precisely. Often you'd see a target/varmint rifle with a 6x internal adjustment scope that had been 'bumped up' to 10x, 12x, or even 18x with a Litschert attachment.