Rules
The following rules are applied by NOAA for sounding rounding:
• For 30.5 metres and deeper, if the decimal part is 0.75 or greater, round to the deeper whole unit.
• For soundings between 21 and 30.499 metres: If the decimal part is greater or equal to 0.875 round to the deeper whole unit. Else if the decimal part is greater or equal to 0.375, round to 0.5
• For soundings 20.999 metres or shallower, if the second decimal is 0.075 or greater, round to the deeper first decimal
• Rounding in fathoms.feet and feet use a single threshold.
• Fathoms and feet are in the format X.YZZZ., where X is fathoms, Y is feet, and ZZZ is decimals of the foot.
• For fathoms.feet shallower than threshold, soundings round to the deeper foot if the decimals of the foot are X.Y75000 or greater. For example, 35.574 becomes 35.5.
• For fathoms.feet deeper or equal to the threshold, soundings round to the deeper fathom if feet and decimals of the foot are X.45000 or greater, because 4.5 feet is equal to 0.75 fathoms. For example, 35.575 becomes 35.6.
Rules for depths below datum (in metres)
Range | Level | Shallowest | Deepest | Direction | Result | |
|---|---|---|---|---|---|---|
0.000 | 20.999 | x.1 | x.y000 | x.y749 | Shallower | x.y |
0.000 | 20.999 | x.1 | x.y75 | x.y99 | Shallower | x.(y+.1) |
21.0 | 30.499 | x.5 | x.375 | x.874 | Shallower | x.000 |
21.0 | 30.499 | x.5 | x.375 | x.874 | Deeper | x.5 |
21.0 | 30.499 | x.5 | x.875 | x.999 | Deeper | x+1 |
30.5 | 9999 | x | x.000 | x.744 | Shallower | x |
30.5 | 9999 | x | x.750 | x.999 | Deeper | x+1 |
For depths below datum in fathoms.feet (x.y)
Range | Level | Shallowest | Deepest | Direction | Result |
|---|---|---|---|---|---|
< threshold | y | x.y00 | x.y74 | Shallower | ff ft |
< threshold | y | x.y75 | x.y99 | Deeper | ff ft+1 |
=> threshold | x | x.000 | x.y44 | Shallower | x.000 |
=> threshold | x | x.y45 | x.599 | Deeper | x+1 |
Rules for drying heights (all units)
Range | Level | Shallowest | Deepest | Direction | Result |
|---|---|---|---|---|---|
-0.001 and shallower | x | -x.049 | -x.001 | Deeper | -x.000 |
x | -x.999 | -x.050 | Shallower | -x-1 |
Example (Metres)
0.1 Level | 0.5 Level | 1.0 Level | |||
|---|---|---|---|---|---|
Depth (m) | Display (m) | Depth (m) | Display (m) | Depth (m) | Depth (ft) |
0.000 | 0 | 21.000 | 21 | 30.5 | 30.5 |
0.001 | 0 | 21.374 | 21 | 30.740 | 30.5 |
0.074 | 0 | 21.375 | 21.5 | 30.750 | 31 |
0.075 | 0.1 | 21.874 | 21 | 30.999 | 31 |
0.099 | 0.1 | 21.875 | 22 | 31.000 | 31 |
0.100 | 0.1 | 30.000 | 30 | 31.749 | 31 |
0.174 | 0.1 | 30.374 | 30 | 31.750 | 32 |
0.175 | 0.2 | 30.375 | 30.5 | 31.999 | 32 |
0.199 | 0.2 | ||||
0.900 | 0.9 | ||||
0.974 | 0.9 | ||||
0.975 | 1 | ||||
0.999 | 1 | ||||
20.900 | 20.9 | ||||
20.974 | 20.9 | ||||
20.975 | 21 | ||||
20.999 | 21 | ||||
Example (fathoms and feet)
Fathoms and Feet | ||
|---|---|---|
Depth (m) | Depth (ff) | Display (ff) |
0.000 | 0.000 | 0 |
1.139 | 0.374 | 0.3 |
1.143 | 0.375 | 0.4 |
1.216 | 0.399 | 0.4 |
53.035 | 29.000 | 29 |
54.784 | 29.574 | 29.5 |
54.788 | 29.575 | 30 |
54.860 | 29.599 | 30 |
54.864 | 30.000 | 30 |
56.232 | 30.449 | 30 |
56.236 | 30.450 | 31 |
56.689 | 30.599 | 31 |
91.440 | 50.000 | 50 |
92.808 | 50.449 | 50 |
92.812 | 50.450 | 51 |
93.265 | 50.599 | 51 |