Absolute limit values provide quick and easy orientation (see Fig. 1). They are, for the most part, based on statistical analyses of machines operated under comparable conditions. As long as these operating conditions are in agreement, the limit values used are also applicable. Under differing conditions, such as start-and-stop versus continuous operation, the absolute limit values lose their significance. For all statistics, limit values must always be validated by experienced experts. If they are set too high, it may be that the lubricant has changed significantly or that the machine has been damaged without this being noticed. If they are too low (see Fig. 2), then the accumulating alarms are eventually ignored, because they occur regularly and often without good reason. Then, when an actual problem does arise, no one will respond quickly enough. Analytical results often show no ideal trend such as that shown in Fig. 1. Rather, the values (see Fig. 3) vary within a certain range, so that several samples (at least 3-4) are needed to form a trend. Only then is it possible to predict the range of values for the next result. It may also be the case that the same values for similar machines but differing trends lead to different recommendations. If the jump in a wear value is too large compared to the previous sample or in relation to the duration of use, an indication will appear in the OELCHECK diagnosis, even if the result of the analysis is below the absolute limit. Particularly when lubricants have been in use for a very long time, limit values can also be exceeded without the necessity of a warning (see Fig. 4). If the increase is in line with the trend and with the expected range for the duration of use, operation may continue without difficulty. The trend supplements the absolute limits by making more in-depth interpretations possible. This improves the predictive quality, and emerging problems are detected even earlier. This is because the trend only takes previous analysis values from the same machine into account, and so specific application conditions can best be considered. It works the same way with the doctor. He compares the results of a blood analysis with their general limit values in relation to the patient‘s personal attributes and life circumstances. The patient‘s medical history, i.e. the trend, is then used for the final assessment.