What does the following error message mean?
Arduino: 1.8.2 (Mac OS X), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"
Sketch uses 3302 bytes (1%) of program storage space. Maximum is 253952 bytes.
Global variables use 324 bytes (3%) of dynamic memory, leaving 7868 bytes for local variables. Maximum is 8192 bytes.
Board at /dev/cu.usbmodem1421 is not available
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.