Hi there, ABDO MAHDY.

Allow me to step in and share some insights on how you can track each unit of the rental building.

Yes, you can use classes to track transactions by units, product lines, or any other meaningful segments in your business. Location tracking is used if you do business in multiple locations. 

When you're ready, here's how to turn on class tracking.

1. Go to Settings ⚙ and select Account and Settings.
2. Select Advanced, then select the Categories section to edit.
3. Mark Track classes.
4. Mark Warn me when a transaction isn't assigned a class. This is optional, but it's good to turn on, so when you look at reports, you know everything got classified.
5. Under Assign classes, select One to entire transaction or One to each row in transaction.
6. Click Save, then Done.

Select One to entire transaction if you don't need to enter a class for each product you sell to a customer. You can save time and assign one class to the entire invoice or sales receipt instead.

Once your settings are in order, you can set up a class list and track transactions by class. I'm adding these articles as a guide.

• Set up your class list
• Organize your customer and vendor transactions by class.

Keep me posted if there's anything else you need about tracking units from the rental building. I'll be right here to help you.