Snell-Pym

You can easily spent £25 on a large spirit level. Even a cheap 60cm one costs £10.

Since I have some plans to build a wall across uneven ground, a long spirit level to check my footings are level is a requirement. But I didn't want to spend a lot of money.

So I went into B&Q and, for £5 plus a few tens of pence, picked up a two-metre length of extruded steel box section, a square tube about 1cm on a side and strong enough to not flex noticeably under its own weight.

And for about £2.70 I picked up a small hand-held magnetic spirit level unit.

Combining the two, voila - for under a tenner, I have a two-metre long spirit level.

And although there's only two vials in the magnetic level unit, it has the functionality of a level with lots of vials, since I can position those two vials at any point along the level I require. So I can have them in the middle, for traditional "is this rubble-filled trench roughly level" checking. Or, when nailing a series of pegs into the ground and wanting them to all be at the same height, I can bring the vials to one end of the steel tube, balance the other end on an existing peg (ideally with a helper to hold it there!), and easily read the vials as I adjust the peg I'm leaning my end of the tube on.

And when I'm sick of building walls, I can store the pocket-sized magnetic level away, and think of something useful to make with two metres of steel square tubing, an arc welder, and a brazing set...