An arrangement for measuring the position of an installation platform in an elevator shaft, comprising: an installation platform being arranged to be movable upwards and downwards in a first direction in the elevator shaft, at least one light source (810, 820) being arranged at a predetermined position in the elevator shaft below the installation platform, said at least one light source (810, 820) producing a vertically upwards directed collimated light beam (LB1, LB2), the arrangement characterized by comprising: at least one primary digital imaging device (650, 660, 670) being arranged on the installation platform, at least one secondary digital imaging device (610, 620) being arranged at a predetermined position on a vertical line above the at least one light source (810, 820) in the elevator shaft above the installation platform, at least one beam splitter (950, 960, 970) being arranged at a predetermined position on a vertical line above the at least one light source (810, 820) on the installation platform, the at least one beam splitter (950, 960, 970) dividing the light beam (LB1, LB2) into two portions, a first portion of the light beam (LB1, LB2) passing directly vertically upwards through the at least one beam splitter (950, 960, 970) to the at least one secondary digital imaging device (610, 620) and a second portion of the light beam (LB1, LB2) being turned 90 degrees towards the at least one primary digital imaging device (650, 660, 670), the at least one primary digital imaging device (650, 660, 670) being arranged to take electronic images of the second portion of the light beam (LB1, LB2) hitting the photosensitive sensor of the at least one primary digital imaging device (650, 660, 670) or of a pattern created by the light beam (LB1, LB2) on a reflective or transparent screen positioned at a distance in front of the photosensitive sensor of the at least one primary digital imaging device (650, 660, 670), the at least one secondary digital imaging device (610, 620) being arranged to take electronic images of the first portion of the light beam (LB1, LB2) hitting the photosensitive sensor of the at least one secondary digital imaging device (610, 620) or of a pattern created by the first portion of the light beam (LB1, LB2) on a reflective or transparent screen positioned at a distance in front of the photosensitive sensor of the at least one secondary digital imaging device (610, 620), whereby the horizontal position of the installation platform in relation to the elevator shaft can be measured from the electronic images taken by the at least one primary digital imaging device (650, 660, 670) and the possible bending of the elevator shaft can be measured from the electronic images taken by the at least one secondary digital imaging device (610, 620). an installation platform being arranged to be movable upwards and downwards in a first direction in the elevator shaft, at least one light source (810, 820) being arranged at a predetermined position in the elevator shaft below the installation platform, said at least one light source (810, 820) producing a vertically upwards directed collimated light beam (LB1, LB2), the arrangement characterized by comprising: at least one primary digital imaging device (650, 660, 670) being arranged on the installation platform, at least one primary digital imaging device (650, 660, 670) being arranged on the installation platform, at least one secondary digital imaging device (610, 620) being arranged at a predetermined position on a vertical line above the at least one light source (810, 820) in the elevator shaft above the installation platform, at least one beam splitter (950, 960, 970) being arranged at a predetermined position on a vertical line above the at least one light source (810, 820) on the installation platform, the at least one beam splitter (950, 960, 970) dividing the light beam (LB1, LB2) into two portions, a first portion of the light beam (LB1, LB2) passing directly vertically upwards through the at least one beam splitter (950, 960, 970) to the at least one secondary digital imaging device (610, 620) and a second portion of the light beam (LB1, LB2) being turned 90 degrees towards the at least one primary digital imaging device (650, 660, 670), the at least one primary digital imaging device (650, 660, 670) being arranged to take electronic images of the second portion of the light beam (LB1, LB2) hitting the photosensitive sensor of the at least one primary digital imaging device (650, 660, 670) or of a pattern created by the light beam (LB1, LB2) on a reflective or transparent screen positioned at a distance in front of the photosensitive sensor of the at least one primary digital imaging device (650, 660, 670), the at least one secondary digital imaging device (610, 620) being arranged to take electronic images of the first portion of the light beam (LB1, LB2) hitting the photosensitive sensor of the at least one secondary digital imaging device (610, 620) or of a pattern created by the first portion of the light beam (LB1, LB2) on a reflective or transparent screen positioned at a distance in front of the photosensitive sensor of the at least one secondary digital imaging device (610, 620), whereby the horizontal position of the installation platform in relation to the elevator shaft can be measured from the electronic images taken by the at least one primary digital imaging device (650, 660, 670) and the possible bending of the elevator shaft can be measured from the electronic images taken by the at least one secondary digital imaging device (610, 620).