Output a string's cumulative slope
Python, 29 bytes



lambda s:ord(s[-1])-ord(s[0])


The sum of the differences forms a telescopic series, so most summands cancel out and
(s1 - s0) + (s2 - s1) + &hellip; + (sn-1 - sn-2) + (sn - sn-1) = sn - s0.

If taking a byte string as input is allowed

lambda s:s[-1]-s[0]


will work as well for 19 bytes.

Test both on Ideone.