Stair Problem ?

Construction of the staircase is complete and it has now been delivered to the house. In order to save a little of the cost, we agreed that we would apply the oiled finish to the staircase ourselves, so it is currently lying on it's side in the basement.

While oiling it, I casually counted the number of steps and got a bit of a shock when I found only 12 rather than the expected 13.

When designing and trying to visualize it, I had reverted to my old friend the Excel Spreadsheet to check the measurements to make sure they fit in the allotted space, as well as meet the regulations. This had allowed me to play with the individual step "rise" and "going" options and work out whether the incline met the regulations (less than or equal to 42 degrees) as well as giving me the overall length and floor to floor height. One of the problems this helped with was being able to visualize the number of steps. The top step is effectively the landing, so does it count as a step or not ?

Once I had got the dimensions right, I printed a copy of the spreadsheet and gave it to the joiner for reference. I assume he has been using it... He explained to me how step 13 (the landing step) would sit on top of the trimmer joist and effectively take the upper weight of the staircase. However, the step he has implemented for this (is is not as deep as the others), is definitely number 12 when counting for the bottom.

I was in two minds whether to say anything at this stage. I composed an eMail to the joiner, but Jan wasn't sure I should send it yet. The joiner's wife had a baby only 4 days ago, so he has a lot on his plate right now and we didn't want to spoil his weekend. However, this is important, so I hit the "send" button and headed for the pub !