Surveying has long used astronomic observations (solar and Polaris) to establish "true" meridians and determine declination for compass direction correction. Burt's Solar Compass was really the first instrument that integrated solar observations with magnetic readings to to reliably determine declination in the field. Surveyor's compasses also incorporated bubbles to allow instrument levelling. As for chaining distances, in some east coast jurisdictions prior to the early 1800s, distances were assumed to be along the ground rather than horizontal (more common in mountainous terrain). Otherwise, the chain was often leveled "by eye." For example, from Surveyor General Jared Mansfield's 1804 PLS Instructions: "In all measurements, the level or horizontal length is to be taken not that which arises from measuring over the surface of the ground, when it should happen to be uneven & hilly, for this purpose the chainman, in ascending or descending hills must alternately let down one end of the chain to the ground & raise the other to a level as nearly as may be, from the end of which a plumb should be let fall to ascertain the spot for setting the tally rod or stick & where the land is very steep, it will be necessary to shorten the chain by doubling the links together, so as to obtain the true horizontal measure."

@@NLCTestPrep Thanks for the clarifications. Respect to the surveyors of yesteryear and today!