Subscripts on depth readings?

[berner73]

Probably a dumb question, but I can't figure it out. On the Navionics charts, occasionally there appear numerical subscripts next to the depth readings. They aren't present on our paper charts or other GPS.

What do these designate? Is it a conversion or tide related measurement? I can't imagine it's a fractional reading (decimal point) as I'd be hard pressed to believe there's that much accuracy or value in that many significant figures.

I was reminded of this after reading one of Sequitur's latest posts (image from that post below). In the area we sail, the subscripts aren't as frequent, much more random.

 

[weinie]

Big number is fathoms, little is feet.

e.g. the sounding just NE of your position is 4fathoms+1 ft = 25 ft.

 

[berner73]

Big number is fathoms, little is feet.

e.g. the sounding just NE of your position is 4fathoms+1 ft = 25 ft.

Thanks. I considered that as well, but there are readings where the subscript is 6? Look just SW of the boat's position.

We set our iPad to feet and it still shows the subscript.

 

[weinie]

Thanks. I considered that as well, but there are readings where the subscript is 6? Look just SW of the boat's position.

We set our iPad to feet and it still shows the subscript.

Sorry,
Its meter and tenths in this case.

 

[berner73]

Tried the obvious and checked the Navionics website. Found this:


Q. How do I interpret the spot soundings found in Navionics charts (meters/feet/fathoms)?
A. The small number is the decimal part of the bigger number. For example: If in "Menu" the user has selected "Meters", then the number 108 means 10.8 Meters (or feet or fathoms, depending on what unit of measure the user selected).

Seemed odd to me, but that's because we normally work in feet. I guess it's more useful for fathoms or meters.

 

[Ross]

This is one of the short comings of chartplotters. You can't slide around and read the entire paper chart where they indicate "soundings in (feet) (fathoms) (meters) (cubits)

 

[LloydB]

IF the original chart was measured in fathoms how do they justify reporting depths in cm. Without reporting the scale on screen that is. Do other chartplotters do similar calculations or is this a function of the actual chart supplier? I may never get one but am interested in how this stuff works.

 

[Ron20324]

...Without reporting the scale on screen that is. Do other chartplotters do similar calculations or....

My chart plotter can be optioned for feet, fathoms, or meters as you chose.