My dad was a civil engineer and registered land surveyor, and we used to run the rod for him when growing up. I remember once being sent several miles away in search of a corner that hadn't been identified in years. He set up on the nearest known point with a theodolite and distance meter (new tech at the time) and kept me moving over the radio until the distance and angle were right. I was on an old pile of rocks...an encouraging sign. We marked the spot and began carefully digging through the rock pile til we found the one marked with the appropriate markings, about a foot from my rod.
He showed me the notes from the original surveyors from the late 1800s. They used rods (16.5 feet, 25 links) and chains (66 feet, 100 links) [5,280 feet in a mile is 320 rods or 80 chains], adjusted for the impact of temperature on its length, and stepped down steep sidehills in increments that allowed the chain to remain level to ensure they were only measuring horizontal distance. As with appraisers and modern surveyors, some cared and were extremely accurate and some were just collecting a paycheck. All such records are signed, so those that follow learn who to avoid,or at least charge more to follow. It seems it is easier these days!