Here is a far easier method. You put your coin in a small paper boat and compute the volume of the boat between the two water levels. Multiplying this by the density of water will give you the weight of the coin. Dead simple, isn't it 
That's the specific gravity method for determining the mass of an object. Usualy a graduated cylinder is used instead of a paper boat, but the latter is a nice touch, and I commend your creativity.
As for the diameter, the second pic of each coin shows my poor little measuring tape tucked in below the coin. The first one is 18 mm (beased on the measurements supplied by Aldo, it looks like a Bazaruco).
I agree. That's a 1 Bazaruco, Copper, 1686, Diu mint. Catalogue references are Gomes P2 02.01, KM 6.
The second one is fatter (close to 24 mm); looks like 2 Bazarucos.
As for the date of the last one, I'm still not certain. Could it be that the date is mirrored? Does 1661 fit in?
The diameter certainly fits a 2 Bazarucos coin. The broader area around the cross and the date also suggests a 2 Bazarucos coin. I think it's safe to assume that the coin is indeed a 2 Bazarucos one. Now for the date. 1661 doesn't fit. Possible candidates are 1669, 1698 and 1699. KM also lists 1679 (KM 3) but that date isn't listed in Gomes, which I trust a lot more than I do KM. 1669, 1698 and 1699 are
not listed in KM. See comment above.
In my humble oppinion, based on the comparison of your pics with the ones in the catalogues, the coin is a Diu mint 2 Bazarucos, copper, 1698 (Gomes P2 03.02) or 1699 (Gomes P2 03.03), KM 12 (unlisted date).
Just my two eurocents worth, I hope Oesho will be able to put our minds at ease.
Aldo
