GRLevel3 Radar Software Key

Filled triangle: Tornado Vortex Signature (TVS)
Hollow triangle: Elevated Tornado Vortex Signature (ETVS)
Red ring: Mesocyclone has been detected
Orange ring: 3CD Shear (weak inner-cloud rotation) has been detected
Filled large triangle: Probability of Severe Hail > 50%
Hollow large triangle: Probability of Severe Hail > 30%
Filled small triangle: Probability of Hail > 50%
Hollow small triangle: Probability of Hail > 30%

From the GRLevel3 Owners' Forum
There are two types of mesocyclone icons in GRLevel3:

1) NMD icons - these are the icons you'll see in GR3 1.40 and above when viewing live L3 data and recent archived L3 data. They come from the New Mesocyclone Detection algorithm in the nexrad computer. When you hover your mouse cursor over an NMD icon, you'll see the following information:

Cell: the storm cell ID associated with the NMD
CircId: id for the NMD
SR: 3d strength rank from 1 (very weak) to 25 (end of the world!)
LLRV: low-level rotational velocity, (Vmax-Vmin)/2
LLDV: low-level delta velocity (gate-to-gate)
Base: lowest altitude of detection ('<' means lowest tilt)
Depth: total height of the rotation ('>' when base has '<')
STMREL: depth of rotation compared to cell heights
MaxRV: maximum rotational velocity in the stack of tilts
hgt: height of MaxRV
MSI: Mesocyclone Strength Index (>3600 is strong)

2) MESO icons - these are the older Mesocyclone Detection Algorithm icons you'll see on archived data and sites that don't output the NMD product. When you hover your mouse cursor over the icon, you'll see:

Type: the type of rotation detected ("Meso" or "3DC Shr")
Cell: the storm ID of the cell closest to the rotation
Base: altitude of lowest tilt containing rotation (ARL)
Top: altitude of highest tilt containing rotation (ARL)
RAD: radial diameter of rotation (nautical miles)
AZD: azimuthal diameter of rotation (nautical miles)
Shear: strength of rotation in the mesocyclone (1/1000 seconds)

"Meso" is shown for rotations that are seen on 3 or more tilts and "3DC Shr" for those that are seen on only 2 tilts.