Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Episode | Broadcast date | Run time | Viewers (in millions) | Archive |
| --- | --- | --- | --- | --- |
| " Episode One " | 30January1971 | 24:39 | 6.1 | Manual colourisation |
| " Episode Two " | 6February1971 | 24:31 | 8.8 | Chroma dot colour recovery |
| " Episode Three " | 13February1971 | 24:30 | 7.5 | Chroma dot colour recovery |
| " Episode Four " | 20February1971 | 24:40 | 7.4 | Chroma dot colour recovery |
| " Episode Five " | 27February1971 | 23:34 | 7.6 | Chroma dot colour recovery |
| " Episode Six " | 6March1971 | 24:48 | 7.3 | Chroma dot colour recovery |
Question:
When there are 7.5 million viewers what is the archive?
Answer:
Chroma dot colour recovery