Let me first explain what does the attached mock do. It's an order manager application where the customer support can go through the orders for a customer. That's what the Customer Order screen does. The app also has different screens, and one of them is the screen to add/update the sales tax for a state. That's what you see on the Sales Tax screen. As you notice, the app has two child screens that can be seen at the same time.
While the user is going through the different orders, he finds out that the sales tax for the state of CA has changed. Nobody noticed the sales tax change in the complex tax system but a Customer Support rep found out about it. He brings up the Sales Tax screen and updates it from 9.2% to 9.5%.
Now the sales tax for the order has changed, so the total for the order has changed. The Customer Order screen should reflect the 9.5% sales tax and the new total.
Here are three options to handle this scenario:
Should the customer support close the Customer Order screen and brings up again (or press the refresh button to refresh it)? The question is, does the app has to expect the user to use the refresh button or take some action to reflect the changes?
Should the Customer Order screen update to the latest sales tax and update the total real time in other words reactive to the changes to the other Sales Tax screen? A nice message can be displayed on the Customer Order screen that the total has changed, so he has to save the order.
Both the Sales Tax and the Customer Order screens should not be allowed at the same time (single screen interface). When the user brings up the sales tax screen, all other screens are closed. When the Customer Order screen is again brought up for the same customer, it will reflect the latest changes.
What I have seen in many desktop apps is the use the first option. I think this approach expects the user to less trust the app. About the third option, there have been discussion about the focus issue of multi screen applications, so use only single screens. In my opinion, using the single screens only increase the navigation and kill the productivity of the user. The web always embraced single page app (eg. google mail).
What does the UX gurus think about the user experience for the three options in this example? Or is there a fourth option?