Rules
The following rules are applied by the IHO M-4 Chart Specifications for sounding rounding:
• Soundings between 0 and 20.999: Rounded to the shallowest decimetre.
• Soundings between 21 and 29.999: Rounded to the next shallowest half metre.
• Soundings 30 metres and deeper: Rounded to the shallowest metre
• All drying heights: Round to the nearest higher decimetre.
Range | Level | Shallowest | Deepest | Direction | Result |
|---|---|---|---|---|---|
Above Datum | -x.1 | -x.y00 | -x.y99 | Higher | -x.(y+.1) |
0.000 to 20.999 | x.1 | x.y00 | x.y99 | Shallower | x.y |
21.000 to 30.999 | x.5 | x.000 | x.499 | Shallower | x.000 |
x.5 | x.500 | x.999 | Shallower | x.500 | |
31.000 and deeper | x | x.000 | x.999 | Shallower | x.000 |
Example
0.1 Level | 0.5 Level | 1.0 Level | |||
|---|---|---|---|---|---|
Depth (m) | Display (m) | Depth (m) | Display (m) | Depth (m) | Display (m) |
0.000 | 0 | 21.000 | 21 | 31.000 | 31 |
0.001 | 0 | 21.100 | 21 | 31.999 | 31 |
0.008 | 0 | 21.400 | 21 | 32.000 | 32 |
0.009 | 0 | 21.499 | 21 | 32.999 | 32 |
0.010 | 0 | 21.500 | 21.5 | ||
0.020 | 0 | 21.800 | 21.5 | ||
0.080 | 0 | 21.999 | 21.5 | ||
0.099 | 0 | 30.499 | 30 | ||
0.100 | 0.1 | 30.999 | 30.5 | ||
0.110 | 0.1 | ||||
0.180 | 0.1 | ||||
0.199 | 0.1 | ||||
0.900 | 0.9 | ||||
0.910 | 0.9 | ||||
0.980 | 0.9 | ||||
0.999 | 0.9 | ||||
20.900 | 20.9 | ||||
20.910 | 20.9 | ||||
20.980 | 20.9 | ||||
20.999 | 20.9 | ||||
Drying Heights Example
Depth (m) | Display (m) |
|---|---|
-0.001 | -0.1 |
-1.000 | -1 |
-2.32 | -2.4 |