MINITAB的解释不清楚的特点大家发现了吗

You work for a textile manufacturer and want to assess the flammability of a new fabric. Testers hold randomly selected pieces of the fabric over an open flame for a fixed amount of time, and measure the length of the burned portion.

You typically use the 87th percentile as a benchmark for such tests. Create a probability plot to determine if a normal distribution fits your data and to estimate the 87th percentile for the population.

这里的87% 基准是什么意思？这个实验怎么能用来做正态分布与否的例子，请大家指教。