8 Small plastic bottles are made from preforms supplied by Britanic Polymers. It is possible that the variability in the bottles is due in part to the variation in the preforms. Thirty preforms are sampled from the extruder at Britanic Polymers, one preform every 5 minutes for two and a half hours. The weights of the preforms age (g).

32.9 33.7 33.4 33.4 33.6 32.8 33.3 33.1 32.9 33.0 33.2 32.8 32.9 33.3 33.1 33.0 33.7 33.4 33.5 33.6 33.2 33.8 33.5 33.9 33.7 33.4 33.5 33.6 33.2 33.6

(The data should be read from left to right along the top row, then the middle row, etc.)
Carry out a cusum analysis of the preform weights and comment on the stability of the process.