It’s often a worry when a play begins by telling you something you learned at school. Tangent opens with one of the cast giving the dictionary definition of the word’s mathematical meaning. This sets the tone for what is to follow.

Two stories are told in alternating scenes. Both concern students who are keen on maths. Sam (Jolyon Westhorpe) is a Midshipman on a naval frigate bound for the Baltic to take on Napoleon’s fleet. He’s hoping for promotion for which he must demonstrate he’s on top of the current techniques of navigation. Chloe (Maisie Turpie) is the new girl in a present-day maths GCSE class, struggling to get herself a B grade in the upcoming exam.

Sam and Chloe are mocked, envied and distrusted by their peers and superiors and must subsequently prove themselves. Sam takes bearings with a sextant and makes complex trigonometric calculations to plot the ship’s position. Chloe learns formulae, calculates angles and plots the values of x and y on a graph. In fact most of the overlong first half takes place in lessons. It’s worthy but not exactly gripping.

In the second half, by contrast, writer Michael Mersea quickens the pace and there’s action aplenty. In the present-day story there are rumours of an illicit relationship between Chloe and her teacher, a teenage pregnancy, a cat fight and a reconciliation. In the past one the frigate comes under enemy attack and Sam saves her from the rocks. But it’s all a bit too much too late.

Director Ed Bartram has worked in schools and with Creative Partnership to teach maths using drama. The play feels like a noble attempt to justify and encourage the study of trigonometry on the basis of its historic importance. In spite of strenuous work from the energetic ensemble to convey the two settings with minimal props and a few funny one-liners, the feeling of tedium emanating from a dull lesson is hard to shake.

- Louise Gooding