Add and remove decimal weights to settle your sub on an exact depth, down to the hundredth.
A target depth is marked on the gauge and your submarine starts elsewhere. Apply weights of 1.0, 0.1 and 0.01 metres up or down to land exactly on the target. A place-value strip splits your current depth into ones, tenths and hundredths so you can see what each move changes.
Decimal Dive teaches decimal place value and precise addition by trimming a submarine to exact depths, where every decimal place matters.
Moving a submarine by weights of 1.0, 0.1 and 0.01 metres, with a strip splitting the depth into ones, tenths and hundredths, is positional notation extended to the right of the point.
The original device is that the place-value strip updates live, so you see which column each move changes.
Decimals are where place value usually breaks down for learners, because the symmetry is imperfect — there are tenths but no "oneths" — and the columns to the right get smaller rather than larger. Watching a 0.01 move touch only the last column is the clearest available answer to that.
Decimal Dive is an original free browser game built for PlayPendium that teaches decimal place value and precise addition through a submarine-trimming challenge. Play free, no sign-up.