## 2 Materials and Methods
### Cost Analysis of the Methods Used  
A comprehensive cost analysis of different methods for evaluating the wear of disc cutters was carried out and is shown in Table 2. The initial investment, the time required for the wear assessment, and the complexity of the measurement methods were evaluated to gain an insight into the cost efficiency and practicability of each method.  
The price range for photogrammetry includes the purchase of a low-cost camera, software, and, if needed, the purchase of high-performance computer equipment for a photogrammetric analysis. Additionally, the caliper method involves purchasing a caliper, while the weighing method entails buying a digital scale for weight measurements. No running costs were incurred, and labor costs are not included in the analysis as these may vary depending on the hourly rate of the measurement personnel.  
All measurements can be performed relatively quickly, within an hour or two, except for photogrammetry, for which the setup and execution take about 5 h. The photogrammetric analysis took approximately 15 h, including pre-processing, for which the time depends mainly on the number of photos and reference and control points, taking about 8 h, and photogrammetric processing, which took about 2 h. It is worth noting that the pre-processing time can be shortened if coded markers are used for reference and/or control points which the software detects automatically on each photo. Additionally, the photogrammetric processing time depends on the performance of the computer equipment.  
The complexity of these methods varies depending on the level of expertise required, the equipment needed, and the intricacy of the procedures involved. The macroscopic inspection method is relatively straightforward, requiring visual observation skills, but may lack precision due to its subjective nature. The caliper method involves using a simple measuring tool and basic mathematical calculations, making it relatively easy to perform with minimal training. Weighing involves operating a digital scale and recording measurements accurately, which is generally uncomplicated. However, close-range photogrammetry introduces a higher level of complexity. It necessitates proficiency in photographic techniques, software operation, and potentially computer hardware setup. Furthermore, the analysis stage, particularly pre-processing and processing, demands meticulous attention to detail and may require advanced knowledge of photogrammetric principles. Despite this complexity, advances in technology and software automation can mitigate some of the challenges associated with photogrammetry, enhancing its accessibility and usability over time.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Initial Investment** &
\begin{tabular}{c} **Required Time for** \\ **Wear Assessment** \\ \end{tabular} & **Complexity** \\ \hline Macroscopic inspection & EUR 0.0 & 1 h & Low \\ \hline Caliper & EUR 800 & 2 h * & Low \\ \hline Weighing & EUR 170 & 1 h & Low \\ \hline Close-range photogrammetry & EUR 650–EUR 3000 ** & 15 h & High \\ \hline \hline \end{tabular}  
* The time required for the wear assessment with the caliper method includes the measurement of 18 profiles of cutter rings on both sides of the double disc cutter with the caliper tool. ** The price, which includes the purchase of high-performance computer equipment and photography accessories for photogrammetric analysis.  
\end{table}
Table 2: Comparison of the cost and complexity of methods for assessing the wear of a disc cutter.