Have you noticed that your overall balance in Wallet changes on it's own? Or, that the balance in a specific account changes even when you haven't done anything to it? This is most likely because you have multiple currencies in one or more of your Wallet accounts.
As you know, you must choose a base currency when you first create your Wallet account. Wallet allows you to create multiple accounts in a variety of non-base currencies as well. However, only a base-currency account can contain Records in multiple currencies. In a non-base currency account, ALL of your Records must be in that currency ONLY. *(Long-term Wallet users, see below!)
For example, Jill's base currency is the euro. In her euro (base currency) accounts in Wallet, she can enter Records in euros, US dollars, Japanese yen, etc. However, if Jill has a yen account in Wallet, then all of her Records in that account must be in yen only.
How does Wallet display Jill's total balance then, if she uses all of these currencies? Wallet displays it in euros, her base currency. To do this, Wallet must convert her yen account balance (and any other non-base currency account balances) to euros using the current exchange rate. (The same goes for those specific accounts with euros, dollars, and yen all in one; Wallet displays the account balance in euro by converting those dollar and yen Records into euro, using the exchange rate.) Since the exchange rate changes on a daily basis, both Jill's total balance and her multiple currency account balances in Wallet may change, too.
*But wait! I'm a long-term user, and I have older multiple currency Records within a non-base currency account! You just said that's not allowed, so what happens?
If you've been using Wallet for a while like Jill has, then you may have a non-base currency account in yen, but with some older Records in that account in dollars. Wallet no longer allows this, but will still calculate your balance for that account in yen. To do this, Wallet will take the USD Record, convert it to the base currency (euro), and then convert it to the account currency (yen). As you can guess, this conversion may affect your balance, as the exchange rate will affect the value of these Records.
So, what can you do? There are a couple of solutions for this issue:
1. You can exclude any one account from the overall stats. This will keep that account from being displayed in your overall balance or in any of your Charts and Reports; it will be totally separate. To do this go into Settings > Accounts > the specific account. Scroll down and tap "Exclude from stats".
2. Create a separate account and move all of the multiple currency Records into that account. Jill could create an account in USD and move all of her USD Records from her yen account into this new USD account. (For bank-connected accounts you'll need to disconnect first.) First, you need to create a new account into which you will move these Records. Then you need to filter out these Records. To choose Records to move into a new account, go to Settings > Accounts > the specific account > Filter icon > Instant filter > select the currency > click on the checkmark to apply the filter.
Once the Records are filtered you will need to long press a Record and a list of options will appear at the top of the screen. Tap on the square icon to select all filtered Records at once. Next, tap on the pencil icon and select the newly created account where you want to move these Records and tap OK.
3. Change the currency of those old Records into the currency of your account. In Settings > Accounts > the specific account, use the instant filter to find all Records in the other currency. You may edit the currency of these Records to match that of the account.