Review on Brix Refractometer with ATC: Essential Hydrometer for Wine Making & Homebrew Kit (0-32% Brix) by Shane Tomko

I purchased this item to measure the amount of sugar in my homemade kombucha. The problem I have is that I keep getting different readings of how much 1 Brix = sugar per 16 oz. For basic calculations I used the following formula: 1 Brix = 1g of sucrose per 100g/solution 100g/solution 3.53 ounces liquid 16 ounces / 3.53 ounces 1 Brix = 4.533 grams of sugar per 16 ounces. Brix at 4.533 to calculate how many grams are in a 16 ounce serving. But then I took readings from two store-bought liquids (orange juice and kombucha). Store-bought orange juice was labeled with 46 grams of sugar per 16-ounce serving. The refractometer read the juice as 11 Brix, which means 1 Brix = 4.18 grams of sugar per Brix). That's an error rate of about 9% compared to the original test - small but enough to make a difference. I then tested store-bought kombucha. The label said a 16-ounce serving contained 10 grams of sugar. The refractometer read the liquid at 4.25 Brix, which means 1 Brix = 2.353 grams of sugar per 16-ounce serving. This is an error of more than 50% compared to my original test of 4.533. Therein lies my confusion. I have three different multipliers: 1 brix = 2.353g of sugar per 16 oz (store-bought kombucha) 1 brix = 4.18g of sugar per 16 oz (orange juice) 1 brix = 4.53g of sugar per 16 oz (sugar water) I have no idea which one to use for my home brew to calculate the sugar content. I understand there will be small differences between liquids due to various factors, but those gaps seem insanely large, especially for an instrument specifically designed to measure the sugar content of more than one specific liquid. Am I missing something? If so, I'll gladly change my rating to 5 stars, but at the moment I can't use the tool as intended and I'm not sure about the issues. Thanks in advance everyone for your help.