## Chapter 9 — Three clocks stay three clocks ### Lesson map Lesson 09. Map, example, EX055. ```mermaid flowchart TD M["about 13:50, remembered"] --> N["The first note keeps it"] B["13:46, advert page"] --> A["A later line adds it"] F["13:48, file time"] --> A N --> Q{"Does the checked time erase the memory?"} Q -->|No| K["Notes add"] ``` Three times describe one afternoon. None of them replaces the others. ### Logical drawing ```text memory about 13:50 browser history advert page 13:46 file time 13:48 note rule add a line do not rewrite the earlier line ``` ### Learning outcomes After this chapter, you should be able to: 1. Name the memory, the advert time, and the file time. 2. Say which line was written first. 3. Refuse a note that deletes "about 13:50". ### 9.1 The checked time is added. The remembered phrase stays. Tomás remembered the download as about 13:50. That phrase is what the first note recorded, beside the 14:20 report. Later, browser history showed the advert page at 13:46, and the file time read 13:48. Priya adds those checked times. She does not go back and replace the remembered phrase with the neater one. A reader who sees only 13:48 has lost the fact that memory and the file disagreed by a small, stated amount. The disagreement is useful. Memory was close, and it was not exact. The file time is the better clock for "when the download landed", because it is a property Priya read, not a reconstruction. The advert time is a different event: a page view, two minutes earlier. Carrier (2005) treats file times as metadata that still need a source. This course does not parse a raw file-system structure. It teaches the three clocks Priya actually wrote down. Priya's later line cites the browser and the file and leaves the volunteer's phrase where it was written. A checker can still see all three clocks. | Clock | Kind of trace | |---|---| | about 13:50 | Tomás's memory, kept in the first note | | 13:46 | Advert page in browser history | | 13:48 | File time Priya read | | One merged clock | Not what the notes contain | ### 9.2 Worked example | Offered note | What it does to the record | Decision | |---|---|---| | First line keeps about 13:50; a later line adds 13:48 and 13:46 | Addition | Keep | | "Correct the first line to 13:48 and delete the memory." | Rewrites an old entry | Refuse | | "The advert and the file are the same instant." | Two minutes apart | Refuse | | All three remain visible | A checker can see the gap | Keep | > **Synthetic case.** The clocks belong to FB-LAP-02's Tuesday. ### Errors and limits Do not sand the remembered phrase down so the file looks perfectly consistent. ### Apply - **EX055 — Three clocks.** Tomás said about 13:50. The advert page is 13:46 and the file time is 13:48. May a later note replace the remembered phrase with the file time? *Rubric:* 3 = no; notes add; about 13:50 stays; 13:46 and 13:48 are added as their own traces;; 2 = the memory stays and the checked times are added;; 1 = one clock;; 0 = none. ### Continue studying — lesson 09 (chapter 09 of 20) [← Chapter 08](#ch-08) · [Course chapter index](../SUBJECTS.md) · [Chapter 10 →](#ch-10) Continue to the next authored lesson. ## Worked answers **EX055.** No. Notes add. About 13:50 stays in the first line. 13:46 and 13:48 are added as their own traces.