[maxmsp] Comparing current value and previous value in a list

hi people!
I need to store incoming acceleration data in some kind of list format, like an array. The list would need to store about 30 incoming values and then eventually empty itself and start again. Would a buffer be better and how would I go about doing this?

Also I need to be able to compare the current value that has just entered the list, to previous int values within the list. Basically say for example that in order for an acceleration value to trigger a sound, it must be above 135. I want to be able to check back to where the last trigger point occurred, if the incoming values in the list start to decrease below the trigger point. I also want to check how much time has passed since the last trigger point. This is a similar idea to a peak finder!

I hope this makes sense! Thanks

A