Thanks for the reply, and explanation beppe! I understand the charging in increments now.

So Wind5 - 1min 15sec call:
16 + 2.5 (first 30) + 2.5 (second 30) + 2.5 (remaining 15 secs) = 23.5
Or 4min... 16 + (2.5 x 8 ) = 36
Super Senza Scatto 4min .... 17x4 = 68