Field cultivator mounted sprayer. Ours was a JD 220 unit mounted on a 4430 in 1973. Most days it was, as you say, very easy to see where you went and easy to control overlap. However, there were days of field cultivating that it was so dry & windy that it was impossible to see the last pass. In those cases it became most easy to use a point on the far end of a 1/2 mile field to guide to, or pick a tree miles away. But, there was overlap and skips. Never had a planter mounted sprayer. We did have granular chem boxes on a 495 putting on Ramrod (corn) and Amiben (beans). I don't think the field cultivator at 4 mph was considered high speed.

Friend drove a pickup mounted sprayer (popular in the early '70s) that used the rope & ball/blade marker working for local ag dealer. Also good as long as there was moisture in the ground. Tougher on dry days with dirt blowing in the same direction you were going.

Counting rows was easy, most of the time when the sprayer was 8, 12 or 16 row configuration. But, on long point rows it was more challenging. Point rows also required more sections and increased workload flipping section switches. Seems back then most of the valves were diaphragm type and subject to a lot of malfunctions for section control. At least ours were it seemed. Motorized ball valves came later.

Counting rows in drilled beans was really difficult for me. Foam markers came along. Great some days, absolutely worthless other days. Great on some days until the sun came out..then the ribbon disappeared.  Seems the foam pumps were also mechanically deficient many times.

Along about that time my friends in aerial application were switching from human flagmen to "mechanical flagmen" which were a piece of cardboard with a paper ribbon attached that fired out of a tube on the upper side of the wing activated by pilot trigger finger. They fell to the surface at the end of the just completed pass. The cardboard and paper was considered as degradable, though they hung around on the surface for weeks. Much better than the kid on the end of the field marking the next pass, but running to get out of the way to not get sprayed.

Note that all above had a real dollar cost, except counting rows.

Then came gps and the world changed. Though Dobson Ag guy challenges my abilities or reasoning to change, I think, like electricity, that gps is one of the greatest things to come along for making farming more precise. The autopilots came along thanks to gps. I used a lightbar for a few years also, but not interested in going back there again either. If we had to return to a "Mad Max" world, I could, but it would be very undesirable. I'm not interested in returning to the 50's, 60s, 70s, 80s, or 90s when it comes to farming methods.

We don't have many skips any longer with planters, sprayers, fertilizer spreaders, N applicators (incl NH3), or other gps stuff. But, since the gps ultimately controls mechanical things...it's possible. 0% overlap is probably mathematically impossible, but it's a lot closer now with nozzle-by-nozzle shutoffs on the newest sprayers.