Compression ratio working???

[Mav122]

Hi all. Just want to check I'm not going mad. Working comp ratios out and my math doesn't seem to add up. Stock comp ratio is meant to be 9.4:1 apparently.
I've done
8.1cm bore
8.2cm head gasket bore
0.12cm crushed head gasket thickness
7.7cm stroke
Pi 3.142
Piston deck clearance 0.05cm (Did deck height (191mm)- conrod length (122mm) - comp height (30mm) - crank throw ie stroke/2 (38.5mm)
So 191-(122+30+38.5) = 0.5mm or 0.05 as cm clearance.

Bore area (bore/2) * (bore/2) * pi = bore area. So 51.536655cm
Gasket bore area (basic same calc as above) = 52.81702cm
Stroke cc is bore area * stroke = 396.8322435 cc
Gasket bore area * gasket thickness = 6.3380424 cc
Piston deck clearance * cylinder bore = 2.57683275 cc
Head is 36 cc
Apparently stock bigport piston cc is -2.5

So add all volumes (cc) up and divide by stroke cc.
This gives 439.2471187 divided by 42.41487515 which is 10.36:1 compression ratio. Is my math wrong or alleged advertised stock piston cc wrong as stock comp is meant to be 9.4:1.
For that stock ratio piston cc would have to be between 2cc & 2.4cc If my calc is correct.

Any input anyone.

[mr2magic]

Using http://www.csgnetwork.com/compcalc.html i come out at 9.79:1

[Mav122]

Just used that calculator and got 9.368480051747252 with my above specs put in. I found solution for mine. I made a calculator on excel spreadsheet similar to the one on that website which I have been using but has been coming up wrong (thus post) but if I use 2.5 instead of - 2.5 it comes up bang on 9.4:1 on mine. Tried same thing for small port 4age where piston Cc is 2.1 but entered it as - 2.1 and compression was spot on at 10.3:1. Basically I have to put a minus value for piston that is plus and Vica versa for a piston that is minus to make it work. Weird. Happy now though.