EH coin classification

I have a 1526 Hungarian 1 Denar that is said to be a EH673a.  What is the EH classification system?  Thank you.  

Hello 🤖

Without pictures, it will be very difficult for anyone to help you. Could you please post clear pictures of each side of your item?

Please note that this is an automatic message. Feel free to ignore if it is not relevant.

When you hover over or click the reference abbreviations in the features box you will get the full name and page in the literature section.
In this case it's https://en.numista.com/literature/volume_group.php?id=59

It's a catalog. Magyar Éremhatározó (Dictionary of Hungarian Coins).

https://en.numista.com/literature/volume_group.php?id=59