How Tall is the Clock Tower?

I was chatting to a girl I tutored last year. She was entered early for her GCSE and we'd been meeting semi-regularly since Year 9 to keep her motivation and interest levels up. Closer to the exam we met once every week and worked through exam papers and I am so pleased to tell you that she got an A in her exam. As a reward, we went for lunch yesterday and for a milkshake - to follow up on the 'If you get a B, I'll take you out for Nandos' promise. Whilst there, she mentioned that her teacher had taken her class outside to investigate with trigonometry. Her exact words were 'It didn't work. No one had a clue what to do. I had to teach them all it'. I don't like the idea of taking my class outside to measure the height of the school, and so I've designed an activity that we can do without leaving the classroom.

I think trig is a very interesting topic and one that can be taken a long, long way. My thoughts about how I'll introduce trigonometry this year is to have groups investigate different triangles and discuss the ratios (poor explanation, but I have a lesson planned and it will go well, I'm sure...) before going on to this activity:

I made an inclinometer today with the help of a straw from the milkshake place yesterday and this resource.

Using this, I went out this afternoon and did some measuring...

I'll cover up the right hand side of this image before we get right into it. I suppose that here we ask if the triangle's the triangle we're supposed to be measuring and maybe get another picture from the side view with the triangle raised to my eye-level.

These were the measurements I took, and may be a little rough as my girlfriend read the inclinometer for me! I intend to have her take some pictures of the inclinometer looking up at the top of the the tower from both distances.

Distance from base of clock tower = 10m, Angle from inclinometer = 23 degrees.
Distance from base of clock tower = 20m, Angle from inclinometer = 40 degrees.

From this we'll get a rough height and be able to answer this question to finish:

Angle from inclinometer = 75 degrees.

Obviously, in between and afterwards they'll get the chance to do a lot of practise.