Job Market has provided you several place to check your units usage and summary of your purchased package, they are: Dashboard, and My Account.
From the Dashboard page, you may find a brief summary of your balance record with all different type of units that you have purchased, such as:
Also, in order to have a better understand of your unit inventory and manage your unit balance, you may find other details such as your unit's order date and the expiry date from Dashboard.
If you want to purchase more units for your instant job posting, Job Market has provided a simple purchasing cart when you find necessary.
From My Account page, you will have a much detail information for all units that you have purchased. It also provides a total balance of unit record from all different valid orders. Please note that Job Market is using First-In-First-Out to deduct your units from Instant Post, Priority Job and Candidate Match.