Some geography students have been conducting environmental geography fieldwork near a busy transport corridor. They were investigating how air quality changes at increasing distances from a major motorway. Some of their results are shown in the table below.
| Sampling Point | Distance from motorway edge | Reading 1 | Reading 2 | Reading 3 |
|---|---|---|---|---|
| A | 20m | 54.2 | 51.0 | 58.7 |
| B | 40m | 38.5 | 41.2 | 39.0 |
| C | 60m | 22.1 | 24.8 | 21.3 |
| D | 80m | 12.4 | 10.9 | 11.5 |
Suggest one problem with the recording of this data.