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158 DE TWEEDE NAUWKEURIGHEIDSWATERPASSING VAN NEDERLAND
to be speeded up. Under normal conditions of levelling the instrument's many possible
adjustments were never utilized, but they did have an unfavourable effect on the stability of
the instrument. The Breithaupt instrument was used in 1923,1925, and 1926, and after fitting
with an optical micrometer was brought back for use by the second levelling team from 193 1.
5.1.2 The Hildebrand level
In 1927 a new instrument was acquired from the Hildebrand company of Freiberg (Fig. 17).
Like the Breithaupt instrument it was fitted with a reversible level ofangle value 5" and a X 40
telescope.
It had a more limited range of adjustments, which made the instrument more stable. The
tripod had a special upper plate (Fig. 15) which made it uncomfortably heavy to manipulate.
In 1930 an optical micrometer was fitted to the instrument.
5.1.3 The Zeiss level: Nivellier A
In 1939 a Zeiss instrument was acquired. Unlike the other two instruments, this one was ofthe
"dumpy-level" type and was already fitted with an optical micrometer. This instrument was
both optically and mechanically more compact and of a more robust construction.
5.2 Staffs
5.2.1 Staffs with Dieperink trapezoidal graduation
At the start of the second geodetic levelling (up to 1930) special staffs were used (Fig. 19),
designed and described by DIEPERINK [3] [4]. The graduations on the 3 metre long staffs were
printed on invar. Practised surveyors can make quick and accurate readings on these staffs;
estimates in units ofO.1 mm can be made. Up to 1930 these staffs were erected with the help of
special staff tripods (Fig. 29).
5.2.2 The invar staff with half-centimetre line graduation
In 1930 the Hildebrand instrument was equipped with an optical micrometer for staff
reading. The Breithaupt instrument followed in 1931.
For this purpose, new staffs with half-centimetre graduations were employed (Fig. 20).
These staffs had two scales, half a centimetre out of line with each other. The readings were
made in half-centimetre units; only after totalling by levelling section was the reduction to
whole centimetres applied.
5.2.3 Special staffs
For reading onto benchmarks a short staff, which could also be used in hanging position, was
available. The Dieperink version was a metre long, the version with half-centimetre line gia-
duations 1.5 metres. For reading onto the ordnance datum benchmarks in Amsterdam a very
special staff was used.
5.3 Miscellaneous
Various auxiliary equipment was transported by. the levelling party in a special handcart
(Fig. 2 1).