TFL Travel Charges. Placement

Before began placement, I calculated that my daily commute would cost around about £16 a day. This was wrong . £12.70 is the most I've been charged for a single days travel. Maybe its because the bus fare is included in the daily maximum charge? Maybe not.
Using £12.70 as the daily cost, I can expect to be paying £254 each month on travel. Much Cheaper than I expected.
What I did today?
Spinal casting, and a lot of it. Today was a Adolescent Idiopathic Scoliosis(AIS) casting clinic at the outpatients centre. I was just helping with the casting. Helping with the casting wasn’t too difficult, but understanding how, when and why the corrective forces are applied is something I'm still getting my head around. I'll have pleanty of time to figure this out, Scoliosis bracing seems to be 30% of the workload here.