Maker

CARL ZEISS, Jena, Germany

Model

5 mm invar line scale staff, 3 m long, with upright numbers

Serial Number

43140

Dimensions

85 x 40 x 3062 mm

Image

Above diagram after Marzahn, K. 1957. Investigations on Invarband Levelling Staffs (Untersuchungen an Invarband-Nivellierlatten), Vol. 22, Series C, German Geodetic Commission (DGK), Verlag der Bayerischen Akademie der Wissenschaften, Munich, Germany.

Description

This type of precise levelling staff was invented around 1913 by Heinrich Wild whilst working at ZEISS in Jena, Germany, from 1908 to 1919, together with levelling instruments with a horizontal wedge on the crosshairs and the Zeiss-Wild measurement procedure for precise levelling (backsight I-foresight I-forsight II-backsight II; BFFB method).

This precision levelling staff features a wooden frame, in which a graduated invar ribbon is suspended under tension. The invar ribbon features two line scales with 5 mm graduation interval. The second graduation is shifted.

The two scales are numbered on the wooden frame from 00 to 60 (units of 5 mm) on the left and from 61 to 120 (units of 5 mm) on the right. Black numbers on white background.

The set up surface at the bottom is made out of steel as is the endplate at the top. The latter contains the tensioning device. The bolts of the tensioning screw are accessible. The tension and, thus, the scale of the invar ribbon can be adjusted. (The adjustment of the staff zero at the bottom is covered and not directly accessible to the user.)

According to a ZEISS catalogue (Ag 21/331/65 9272) "the maximum deviation of any graduation from the true distance to the bottom face of of the staff is 0.05 mm" and "the error of graduation line spacing" is less than 0.02 mm.

To use this staff, the spirit or automatic levelling instrument must be equipped with a plane parallel plate micrometer with 5 mm range. The difference between the readings on the two scales is (within measuring accuracy) constant and is used as a check. For example:

left scale (I) = 377.31 (cm/2), right scale (II) = 983.81(cm/2)

Check: (II) - (I) = 606.50 (cm/2)

The staff features a spot bubble (attached permanently) and two handles that can be folded onto the backface for transport.

When booking levelling runs with two-scale 5 mm invar staffs, the backsight and foresight reading are booked for both scales. The height difference is then computed separately for the left (I) and the right (II) scales. The difference between these two values should be within the usual measuring errors. (At UNSW, a tolerance of 0.06 (cm/2) (= 0.3 mm) was used for student exercises.)

History & comments

This staff was widely used for student exercises in the 1970s and 1980s in conjunction with ZEISS Ni2 automatic levels with 5 mm plane parallel plate micrometers.

Conservation

no case

Condition

Paint damage on front face. Some screws missing. Bent aluminium handle. The invar ribbon is in good condition. The sides and the back of the staff were painted orange at UNSW.

Remarks

Felt pen markings on back: "s/n 43140", "5 mm", "3A"

School of Surveying label

Dates

Catalogued on 25.3.2013 by JMR. Photo by JMR.