Get copies of your quarterly statements from the publisher or company paying the royalties. These statements will give you the most accurate snapshot of what your royalties are at the end of each quarter or bi-annual period. Use statements to track cumulative royalties from sales.
Contact your agent or manager periodically for a royalty number. This number will be less accurate than the one on your statements as it may not reflect sales or uses from all sources. However, it will give you an idea of how well your product is currently performing.
Ask the company or clearinghouse paying the royalties for an audit. Depending on the letter of your contract, you may be entitled to an audit upon request. Prepare for the result. It will be a stack of sales logs that are a far cry from the royalty statement you are used to. You will have to compute the royalties from the documents on your own.