| Wrong quantity | What it looks likeThe instrument measures something other than the intended quantity. For example, a sensor sits in the wrong soil layer, or its range percentage is mistaken for a percentage of the monitored quantity. | Why it is not seen in the dataThe readings are steady and plausible. |
| Wrong units or scaling | What it looks likeA conversion, offset or range is wrong at the instrument, the logger or the processing step. | Why it is not seen in the dataThe readings are steady and plausible. |
| Uncontrolled change | What it looks likeA logger is reprogrammed, a sensor is swapped or a processing step is edited. The alarms, reports and users that depend on it are not updated. | Why it is not seen in the dataThe readings continue. The alarms are silent. |
| Uncontrolled access | What it looks likeA supplier or a former employee can reach a component, and no one on site knows who can. | Why it is not seen in the dataNo sign appears until the access is used. |
| Outage in the event | What it looks likeThe station loses power, communications or the instrument itself during the event it was installed to measure. | Why it is not seen in the dataThe readings stop, which is seen, but too late. |
| Drift | What it looks likeThe instrument moves away from the true value over time. | Why it is not seen in the dataThe instrument's drift is mistaken for a change at the site. |
| Unnoticed gap | What it looks likeReadings stop or arrive late and no one is told. | Why it is not seen in the dataNo one checks for missing readings. |
| Unknown path | What it looks likeNo one can name the components between the instrument and the display. | Why it is not seen in the dataA fault in an undocumented part of the chain cannot be located. |