1. Database differences: Different paper duplicate checking systems use different databases, including academic journals, dissertations, Internet and other published literature resources. These databases may be updated and maintained at different frequencies, which will lead to different detection results.

2. Algorithm: Different paper duplicate checking systems use different algorithms. These methods may have different weights, thresholds, rules and logical judgments, so they will produce different detection results.

3. Citation processing mode: The paper duplication checking system may process citations and references in different ways. Some systems may exclude citations and references from the scope of detection, while others may include them in the scope of detection. This difference will also affect the consistency of test results.

4. System settings and parameters: Different paper duplicate checking systems may have different setting options and parameter adjustments, such as similarity threshold and citation processing. Differences in these setting options and parameters may affect the detection results of the system.

When choosing a paper duplicate checking system, we need to carefully choose a formal and legal system, such as papertime recommendation, and pay attention to the format requirements of the paper, the handling methods of cited documents and other details.