title: Unusual syntax for a #define directive
body: <p>In a sketch I found the following instruction:</p>
  <pre><code>#define USB_CONFIG_POWER_MA(mA)                ((mA)/2)
  </code></pre>
  <p>And I want to be sure not to make any mistake: why are there two &quot;mA&quot;?</p>
  <p>Which one should I replace by a value given that in a previous version of this code one just needed this line:</p>
  <pre><code>#define USB_CONFIG_POWER_MA(20)
  </code></pre>
  <p>to set the max to 20mA but now it gives a compilation error:</p>
  <pre><code>/home/henry/arduino-1.8.16/hardware/arduino/avr/cores/arduino/USBCore.h:99:29: error: &quot;20&quot; may not appear in macro parameter list
  </code></pre>
  <p>This seems to be the solution as it gives me no compilation error</p>
  <p>#define USB_CONFIG_POWER_MA(mA)                ((40)/2)</p>
  <p>but again i want to be sure!</p>