Question 1

What is the difference between rise-&-fall and height-of-instrument (HI)? Which should I use?

Accepted Answer

Both give the same reduced levels; they differ in the check they provide. Rise-&-fall takes each reading’s difference from the previous one and offers a full check: ΣBS−ΣFS = ΣRise−ΣFall = ΔRL, so it verifies every point — best when there are many intermediate sights. HI computes the line-of-sight level (HI = RL + BS) and subtracts each fore/intermediate sight from it; it is faster to compute but its check (ΣBS−ΣFS=ΔRL) does not verify the intermediate sights. Use rise-&-fall for rigour, HI for speed when intermediate sights dominate.

Question 2

What arithmetic checks does the tool show?

Accepted Answer

The core check is ΣBS − ΣFS = ΔRL (last RL minus first RL). In the rise-&-fall method a second check is added: ΣRise − ΣFall = ΔRL. Agreement proves the additions and subtractions are correct — but it does not catch a misread staff; that is why the closure check still matters.

Question 3

How is the allowable misclosure ±k√K computed?

Accepted Answer

The misclosure is the computed final RL minus its known value. The allowable is ±k·√K millimetres, where K is the run length in kilometres and k is the order-of-work constant (we use 12 mm/√km for ordinary levelling; precise work uses smaller values). If the misclosure is within the allowable, the run is accepted.

Question 4

How is the closure distributed over the points?

Accepted Answer

The misclosure (with the opposite sign) is spread equally across the instrument setups — the change points that carry a fresh backsight — so corrections accumulate progressively until the final point lands exactly on its known RL. The “Adj. RL” column shows the levels after this distribution.

Question 5

What is a change point?

Accepted Answer

A change point is a station carrying a foresight (FS) to the old instrument position and a backsight (BS) after the instrument is moved — the start of a new setup. Enter both an FS and a BS on the same row to define one; the tool detects it and distributes the closure over these setups.

#	Point	BS	IS	FS	Remove
1
2
3
4

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