what equipment do i need to measure the carat weight for the gems in test 4?
Digital scale. Get one accurate to 0.02 ct, at least, because accurate weight is important in determining value, esp. with valuable stones. Also, if you use the scale to determine SG on small specimens, you want all the accuracy you can get.
Some very convenient and cheap digital scales available (check ebay), but the cheaper, smaller models don’t measure over 50 cts, if this is an issue. It can be if measuring rough stones.