I have ended up buying two hydrometers. I first called Plymouth Battery Centre who informed me they had a glass model at £19 which I thought was a bit expensive so when I went to town I thought I'd look around before I took the mile or more walk to Prince Rock.
The Toolshed could get a glass model for £5 and the car shop next door had the same model for £2.99, which I bought. When I went to the Plymouth Battery Centre to buy some red and black covered multi-core cable I decided to buy the hydrometer they had anyway, which cost £14.50 eventually.
The better model from Plymouth battery Centre is the one on the left, although you cannot see the coloured scale. It is supplied by Gordon Equipments under the name DURITE model 0-070-00 ; range 1.15 to 1.40; accuracy 0.01. All parts are individually replaceable.
Concerns regarding the cheapo
- The float diameter is much smaller than the container diameter so the readings are at an angle.
- On the side of the container the float rests, the surface tension of the acid draws the liquid further up the side of both, giving a distorted view.
- The scale is on the small side so not so easy to read.
- And of course there's the idea that the calibration is off.