(b) (a) (c) FIGURE 3. The coffee machine's water tank level is encoded in the foliage density. Three levels are considered. (a) Low-density foliage is displayed if the tank is less than one-third full. (b) Medium-density foliage represents a water level that lies between one-third and twothirds full. (c) Dense foliage indicates that the tank is more than two-thirds full. (b) (a) FIGURE 4. The foliage color encodes the machine temperature. Two states are considered. (a) The tree with green leaves represents the temperature being within the operational range. (b) The tree with red leaves indicates that the temperature is not in the operational range. (b) (a) 2) Temperature is represented by the leaf color (Figure 4). We considered two states: green leaves if the temperature is within the operational range (20-60 °C), and red leaves if it is above or below that. 3) The number of cups of coffee that have been made is represented by the presence or absence of magnolia flowers, as shown in Figure 5. The number of coffees brewed indicates when the machine requires upkeep (its maintenance status). The absence of flowers means that the machine is running under duress because a cleaning is long overdue. The presence of flowers indicates that the machine is operational. The size of the flowers denotes when the next maintenance episode is required. We encoded three possible states: small flowers indicate that a cleaning will be required soon, medium-size flowers point to an intermediate state, and large flowers signify that the machine will not require maintenance for a while, possibly because upkeep has just been performed. (c) (d) FIGURE 5. The flower size encodes the time to the next maintenance episode. Four states were considered. (a) The tree has no flowers if the machine's maintenance is long overdue. (b) and (c) Intermediate states of the coffee machine are represented by intermediate flower sizes. (d) The tree has large flowers if the machine was just serviced. 94 IEEE Consumer Electronics Magazine ^ MAy 2018