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Figure 3.1. When Bob opens the Smart Grid application, he sees a graph of his usage for today. By touching the "month" tab at the left of the graph and looking at the average at the top right, he sees that his usage for today is much greater than his average usage over the past month. He returns to the "day" tab of the graph and notes, by expanding the tree in the bottom pane, that his air conditioner is consuming most of the power. He unchecks the boxes for all devices except for the air conditioner, which updates the graph to show only the air conditioner's power usage for the day. By doing so, he sees that the highest usage was during the afternoon.

Pros: 
The tabbed display is a familiar paradigm, especially on mobile devices.

The expandable tree used to display the devices is also familiar from other applications.

The graph is intuitive to use, and tabs, titles, and axis labels make clear what information is being displayed.

Cons: 
The use of the checkboxes in the lower pane to update the graph may be unintuitive.

It may be unclear what the usage numbers in the bottom pane correspond to: are they the current usages? averages for the day? Additional labels would be helpful to disambiguate this information.

Pros: 
The opening screen is easily glanceable. The information likely to be most important to users, the current power usage, is displayed immediately when the application is opened.

The organization of devices into a tree allows the interface to scale well, efficiently supporting operations on large numbers of devices.

Cons: 
The user may have to check and uncheck many boxes in order to display the desired information in the graph.

The devices device list cannot be sorted by power consumption; some exploration of the tree may be required in order to determine which devices are using the most power.

Pros: 
It is clear how to undo actions in this pane, such as checking a box or selecting a tab.

Cons: 

Figure 3.2. Bob touches the "grid" tab to view today's pricing information. Simply glancing at the shape of this graph allows him to tell it is a peak usage time. The current price is displayed on the "grid" tab, and can also be viewed by touching the current time on the graph itself.

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The graph view and split-pane interface of this screen is internally consistent with the others.

Cons:
The application requires some background knowledge about the way the grid operates and the way power is priced. Non-expert users without such background knowledge may find it difficult to understand the information presented without more context.

Pros:
The pricing information is easily glanceable.

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Figure 3.3. To change the settings of Image Removed
Figure 3.3. To change the settings of his air conditioner, Bob first navigates back to the "usage" tab (Figure 3.1), then clicks the "settings" button for the air conditioner. The top pane displays a graph of the air conditioner's power usage for today, helping Bob decide what settings to change in the bottom pane. He uses the spinner to increase the setpoint of the air conditioner. He then presses "save" and is returned to the screen in Figure 3.1.

Pros: 
The spinners used for numeric data entry are standard Android widgets, familiar from other applications.

Spinners are populated with default values, which-, together with the up and down arrows-make , make clear what kinds of inputs are permitted.

Cons: 
Pros:
By using spinners to change device settings, the application may lose external consistency with the way those settings are entered on the devices themselves.

Pros: 
The graph is automatically updated to display daily view, which is presumably the  
The graph is automatically updated to display daily view, which is presumably the information that is most relevant to the settings being changed.

After the settings are saved, the graph returns to displaying the data that was previously selected.

Cons:
It is not possible to view data for other devices while changing the settings of a device. If the user wants to take this information into consideration, they will have to go back to the main usage screen to see it.

Since the graph is automatically updated to the daily view, if the user was interested in looking at usage over the last week or month, they will have to readjust the graph after entering the settings screen.

Pros: 
The "cancel" button allows the user to revert any changes they have made to the settings.

Cons: 
There is no indication of whether the settings have been modified, so a user may end up saving an inadvertent change.

Figure 3.4. Bob checks the status of his power storage device by touching the "storage" tab. He glances at this screen to see both the current amount of stored power and the historical amount of stored power for today.

Pros: 
The graph view and split-pane interface of this screen is internally consistent with the others.

Cons: 
As with the "usage" screen, the checkboxes may be unintuitive to use, and the numbers displayed in the devices list may be ambiguous without additional labels.

Pros:
This screen, too, requires only a quick glance to determine the needed information.

Cons:
As with the "usage" screen, devices are not sorted by amount of stored power, and much checking of boxes may be needed to display the desired information.

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It is clear how to undo actions in this pane, such as checking a box or selecting a tab.  
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Figure 3.5. To schedule a sale of power, Bob returns to the "grid" tab (Figure 3.2), then touches the "schedule transaction" button. He uses the spinners to adjust the time and the amount of power to be sold. He uses the pricing graph in the top pane, and the total amount of stored power displayed on the "storage" tab, to help him decide. He touches the "save" button and is returned to the screen in Figure 3.2, which now lists the scheduled transaction.

Pros: 
Again, the use of spinners is familiar from other applications, and makes clear the kinds of inputs which are allowed.

Cons: 
The interface does not expose all underlying details of the grid and of power transactions. A non-expert user may not know how to decide on the parameters of a transaction, and may not understand where the power goes or how they are paid for it.

Pros: 
The data displayed at the top of the "storage" tab allows the user to decide how much power to sell without having to switch back to that tab.

Cons: 
Previously scheduled transactions cannot be viewed from this screen. If the user wants to take this information into account, they will have to return to the main grid page to see it.

Pros: 
Transactions take place at a scheduled time rather than happening instantly, so they can be modified or cancelled in case an error is made.

Cons:
The user receives no suggestions about how much power to sell or when to sell it, so a non-expert user could make a poor selling choice.

Critiques of the overall design

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Cons:  - similarity of each pane provides internal consistency
- familiar widgets: spinners, trees, graphs
- clear text labels show what data is being displayed

Cons: 
- where labels are absent, can be ambiguous what the numbers mean
- for some actions, users need knowledge of underlying grid system

Pros: 

- attempts to display the most relevant data for the current decision being made

Cons:
- no consolidated view of all data
- annoying to user if automatically-selected view is not the one that is desired

Pros:
- use of tabs, widgets, and transaction scheduling makes it clear how to undo most actions
- use of input widgets prevents invalid inputs

Cons: 
- lack of suggestions from the application means non-expert users may make poor decisions