## 1 Introduction
### Wear Measurement Methods
#### 1.6.4. Profile Measurement Using a Profile Gauge/Wear Ruler  
In addition to the techniques mentioned above, profile measurement using a profile gauge is another frequently used method for assessing the wear of disc cutters. A profile gauge, also known as a wear ruler or measuring template, is a special tool for measuring the profile wear of a disc cutter. The profile gauge consists of a molded template or ruler with a specific contour that corresponds to the original shape of the profile of the disc cutter. By placing the gauge against the worn surface of the cutter, engineers can visually compare the shape and depth of the wear profile with the template.  
Profile measurement using a profile gauge is a quick and practical method for assessing the wear condition of disc cutters, especially for visual inspection. It is often used in conjunction with other measurement methods to gain a comprehensive understanding of wear behavior. Several studies [18, 19, 20, 21, 38, 42, 53, 54] use or mention profile gauges for wear assessment.  
[PERSON] et al. [20] investigated the basic process of disc cutter wear during the construction of the first 6500 m of Tehran Metro Line 7 in soft ground using an earth-pressure-balance TBM. The aim of the study was to understand the effects of soil properties and operating factors on disc cutter wear using a profile gauge. In a study by [PERSON] et al. [19], the extent of disc cutter wear was measured in millimeters using a profile gauge. The worn cutters were properly adjusted to ensure that the difference in cutter ring wear between adjacent cutters was less than 15 mm. This systematic measurement and recording of wear data made it possible to track the wear progression of the cutters and determine when they had reached their allowable wear limit or exhibited abnormal wear that required replacement. [PERSON] and [PERSON] [18] investigated the effect of rock abrasiveness on the wear of disc cutters and slurry discharge pipes in a slurry-shield TBM during tunnel construction in Singapore. The study involved measuring and monitoring the radial wear of disc cutters and the thickness of slurry discharge pipes using specialized tools such as wear rulers and ultrasonic measuring devices. Cerchar abrasivity index (CAI) values were correlated with the wear coefficients of the disc cutters and the carbon steel slurry pipes. These correlations helped the researchers understand the relationship between the degree of weathering of the Bukit Timah granite and the wear rates of the excavation equipment. [PERSON] et al. [38] used a special ruler as a measuring tool to measure the depth of normal wear on a cutter. Similarly, [PERSON] et al. [42] used a measuring template to measure the amount of material lost from the tip or cutting edge of a disc cutter.  
Although the authors do not explicitly report the disadvantages of using profile gauges, special rulers, or measuring templates to determine the wear of disc cutters, possible limitations such as inaccuracies, subjectivity, and time-consuming manual methods can be considered. These factors can lead to errors, incomplete data, and inconvenience in the measurement process. This emphasizes the importance of exploring advanced and automated measurement systems for greater accuracy.