It should read 2". Strangely there are no stability problems as well...
I might be wrong, but it looks like you use metric for your armor and not imperial, so shouldn't it be 20mm?
Also, this is what I get when I enter the data of your ship:
Panthera, Italian Light Cruiser laid down 1917
Displacement:
3,515 t light; 3,632 t standard; 3,856 t normal; 4,019 t full load
Loading submergence 333 tons/feet
Dimensions:
444.40 ft x 44.30 ft x 15.00 ft (normal load)
135.45 m x 13.50 m x 4.57 m
Armament:
8 - 4.72" / 120 mm guns
4 - 3.00" / 76 mm AA guns
Weight of broadside 476 lbs / 216 kg
2 - 21.0" / 533.4 mm above water torpedoes
Armour:
Main gun shields 0.79" / 20 mm
Conning tower 2.95" / 75 mm
Machinery:
Oil fired boilers, steam turbines,
Geared drive, 2 shafts, 42,621 shp / 31,795 Kw = 30.50 kts
Range 6,000nm at 10.00 kts
Complement:
244 - 318
Cost:
£0.712 million / $2.849 million
Distribution of weights at normal displacement:
Armament: 59 tons, 1.5 %
Armour: 26 tons, 0.7 %
Belts: 0 tons, 0.0 %, Armament: 10 tons, 0.3 %, Armour Deck: 0 tons, 0.0 %
Conning Tower: 16 tons, 0.4 %, Torpedo bulkhead: 0 tons, 0.0 %
Machinery: 1,562 tons, 40.5 %
Hull, fittings & equipment: 1,868 tons, 48.4 %
Fuel, ammunition & stores: 340 tons, 8.8 %
Miscellaneous weights: 0 tons, 0.0 %
Metacentric height 2.0
Remarks:
Hull space for machinery, storage & compartmentation is cramped
Room for accommodation & workspaces is excellent
Ship has slow, easy roll, a good, steady gun platform
Estimated overall survivability and seakeeping ability:
Relative margin of stability: 1.19
Shellfire needed to sink: 2,495 lbs / 1,131 Kg = 47.3 x 4.7 " / 120 mm shells
(Approx weight of penetrating shell hits needed to sink ship excluding critical hits)
Torpedoes needed to sink: 0.6
(Approx number of typical torpedo hits needed to sink ship)
Relative steadiness as gun platform: 70 %
(Average = 50 %)
Relative rocking effect from firing to beam: 0.18
Relative quality as seaboat: 1.15
Hull form characteristics:
Block coefficient: 0.457
Sharpness coefficient: 0.32
Hull speed coefficient 'M': 8.66
'Natural speed' for length: 21.08 kts
Power going to wave formation at top speed: 59 %
Trim: 61
(Maximise stabilty/flotation = 0, Maximise steadiness/seakeeping = 100)
Estimated hull characteristics & strength:
Underwater volume absorbed by magazines and engineering spaces: 143.0 %
Relative accommodation and working space: 139.6 %
(Average = 100%)
Displacement factor: 106 %
(Displacement relative to loading factors)
Relative cross-sectional hull strength: 1.16
(Structure weight / hull surface area: 90 lbs / square foot or 438 Kg / square metre)
Relative longitudinal hull strength: 1.97
(for 16.50 ft / 5.03 m average freeboard, freeboard adjustment 3.98 ft)
Relative composite hull strength: 1.22
Walter