It really does look very much like a parking meter of the time, and the joke doesn’t really make sense unless it’s a parking meter. It’s a rent-seeking/capitalism gag.

• The caveman on the left, is creating something transformatively useful, that once finished will change his life with how useful it is. Aka he’s inventing the wheel.
• The caveman on the right is creating something that will act as a small but annoying tax on the work of the caveman on the left… doing nothing of intrinsic value but making the real invention a little bit less useful and helpful by charging the very first wheel for parking. Aka he’s inventing useless self absorbed beauracracy, mankind’s second most significant invention after the wheel.

The gag establishes the relationship between the two cavemen as a doer on the left and a beauracratic leech on the right. If the right is a scale, there’s kind of nothing going on here. Not that there aren’t far side comics where nothing is going on, but this one has a gimmick.

Different time I guess. Maybe parking meters looked like that back then

It’s definitely a parking meter