the custom bottles only take two price observations: your buy price and the latest price observations you have. Hence they do not allow for tracking the price development. Only the relative change from your buy price to the latest price is considered. When you update the latest price observation it will be set to the current month with the value you typed in.
How many decimals did you try to enter? It should allow for two (e.g. 40,63% vol). It also should accept both comma (“,”) and point (“.”) as the decimal sign. But maybe you could try both.
Johannes from Whiskystats