The pour point is the lowest temperature at which a petroleum product will begin to flow. Pour point is measured at intervals of 5o F. This interval gives a range in which to account for error inherent in the measuring procedure. A sample with a pour point of 10.5o F and a sample with a pour point of 14.5o F would be labeled as having a pour point of 15o F. Even with the 4o difference they would be considered the same. However, a sample with a pour point of 15.5o F would be labeled as having a pour point of 20o F even though it is only 1o higher than the 14.5o F sample mentioned before. Due to experimental and operator error, sample variations of one interval are not considered significant. Since the measured values for the two samples are only one interval apart the difference is not significant.
The cloud point is the temperature at which wax crystals begin to form in a petroleum product as it is cooled. Cloud point is measured at intervals of 2o F. An example similar to the one used illustrating the pour point procedure applies here. Differences of one interval are not considered significant. Wax crystals depend on nucleation sites to initiate growth. The difference in the cloud points of the two samples is explained by the fact that any fuel additive will increase the number of nucleation sites, which initiate clouding. A change in temperature at which clouding starts to occur is therefore expected upon addition of any additive. The difference between the cloud point values for the two samples is not abnormal and is not significant.