A manual instrument requires an operator at the instrument and a second person at the target. A robotic instrument tracks the prism automatically and is controlled remotely from the pole, so one person does the whole job. On setting-out work that halves the labour, which is usually what justifies the higher price.

Measuring distance directly to a surface rather than to a prism, which allows survey of facades, steelwork, rock faces and anything unreachable or unsafe. Range and accuracy are both lower than prism measurement and depend strongly on the surface colour and texture and on the angle of incidence.

In seconds of arc, with a smaller figure meaning a more accurate instrument. Because an angular error becomes a linear error that grows with distance, the specification matters most on long sights - a one-second and a five-second instrument differ little at short range and considerably across a large site.

Establishing the instrument's own position by observing two or more known points, rather than setting up over a known station. It lets the instrument be placed wherever the sight lines are best rather than where a control point happens to be, which is often the difference between a workable setup and an impossible one.

Prism measurement works in darkness and is largely unaffected, which is why night work is practical. Reflectorless range drops in rain, fog and heavy dust because the beam is scattered. Instrument environmental rating governs whether it can be used at all in sustained wet conditions.

Setup over the control point and levelling first, then a check shot to a second known point before any production work - this catches a wrong instrument height, a mistyped coordinate or a disturbed control point, which are the errors that otherwise propagate through everything set out that day.

No, they cover different conditions. A total station works indoors, under structure and in obstructed sites where GNSS cannot, and is more accurate. GNSS covers open ground quickly without sight lines. Most site survey uses whichever suits the environment, often both on the same project.