Today I'm restoring a Star Adding Machine made by the Todd Protectograph Company in 1925 or early in 1926. Later in 1926 these machines were redesigned and sold as the Todd Visible.
Here is a view of the machine from the front, and a look at the internal mechanisms. A few of the input registers were pretty sticky and as a result wouldn't reset properly so I spent some time oiling and working those mechanisms to loosen things up.
Here is what it looks like after restoration and cleaning. There is a hinged lid that can come down to protect (and even lock) the adding machine when it's not in use.
Like other simple adding machines you subtract by the complements method. Use the tiny digits next to the larger digits for the subtrahend. The red buttons along the top prevent the carry mechanism. Here's 1000-1, which you get by adding 9999.
The red lever on the side is used to clear the registers. All of the registers are spring-loaded on the inside so resetting them is fast (when they are oiled properly).
All in all this is a nice little adding machine, if a bit limited. The cover and carrying handle is a nice touch.
Adding is similar to on a chain adder like the Gem Pocket machine I featured earlier. In this case instead of a stylus, you put your finger next to the corresponding lever and pull all the way down to add the digit to the register.