How does Holmes determine the date of manuscript?

You're likely referring to the short story "The Adventure of the Dancing Men," where Sherlock Holmes uses his keen observation and deductions to determine the date a manuscript was written. However, he doesn't use any specific method to determine the exact date. Instead, he focuses on the style and content of the manuscript to draw inferences about its age:

* Paper: He notes that the paper is "of a peculiar kind, thin and almost transparent" which was "not common in this country" at the time. This suggests the manuscript was likely written in the past, perhaps with paper imported from another country.

* Ink: Holmes doesn't explicitly mention the ink, but he might have observed the shade or its chemical composition to determine if it was common for a specific period.

* Writing style: The manuscript is a series of "stick-figure" pictograms. This specific style might have been popular at a certain time or might have been unique to a specific individual, allowing Holmes to infer its age.

* Content: The content itself can be an indicator of the manuscript's age. The story depicts a coded message that, based on its content and themes, could potentially be tied to events or cultural trends of a specific era.

In short, Holmes uses his knowledge of paper types, writing styles, and the historical context of the content to deduce the approximate date of the manuscript. He doesn't rely on a single method but rather combines various observations to arrive at his conclusion.