[R] assessing data variation

[e-letter]

I have data like so:

time	datum
30	12
60	24
90	37
120	41
150	8

In addition to standard deviation, I want to measure the average of
the differences in data for each time interval, i.e. average of 24-12,
37-24, 41-37, 8-41. Is there a statistical term for this task? Which
package should I use please?

rhelp at conference.jabber.org