PURPOSE: To prepare the quality control data with the arbitrary number of the data, by setting the upper limit value and the lower limit value of preset size based on the reference value of a material to be measured and the number of divisions, by which the range of the preset size is divided equally, and memorizing the frequencies of the measured data belonging to the divided sections.

CONSTITUTION: A digital display type length measuring system is composed of a micrometer 1 as a length measuring means and a data processing device 2 as a data processing means, which sequentially receives the measured length value data from the micrometer 1 and obtains the quality control data and the like from the received measured length value data. The data processing device 2 stores the upper limit value and the lower limit value of a preset size based on the reference value of a material to be measured and the number of divisions, by which the range of the preset size is divided equally, in advance. The frequencies of the measured value data belonging to the divided sections is stored. When the specified output starting conditions are satisfied, a histogram is displayed.