Page 194 - Learn To Program With Scratch

Hour sprite
Min sprite

Sec sprite
Time sprite

Figure 7-20: The Analog Clock application

The clock starts running when the green flag is clicked. In response, all
four sprites start a forever loop to update their status based on the current
system time. The scripts for the Sec and Min sprites are shown in Figure 7-21.

Script for the Sec sprite Script for the Min sprite

Figure 7-21: The scripts for the Sec and Min sprites

The number of seconds and minutes reported by the current block
ranges from 0 to 59. When the system reports 0 seconds, the Sec sprite
should point up (toward 0°), at 15 seconds, the Sec sprite should point
right (toward 90°), and so on. Every second, the Sec hand should turn 6°
(360° divided by 60 seconds) clockwise. A similar reasoning applies to the
Min hand. If you watch this clock running, you’ll notice the Sec hand jump-
ing every second and the Min hand jumping every minute. Now, let’s look
at the script for the Hour sprite, shown in Figure 7-22.

hour angle
---- ----
-
0 0
1 30
2 60
... ...
11 330
12 360
13 390 (or 30)
14 420 (or 60)
... ...

Figure 7-22: The script for the Hour sprite

172 Chapter 7
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