m. Then, as they come off the database to be used for a report, they are converted into a target
            unit, specified by the skin. </p>

        <h1>Value &quot;<span class="code">None</span>&quot;</h1>

        <p>The Python special value <span class="code">None</span> is used throughout to signal a missing data point.
            All functions must be written to expect it. </p>

        <p>Device drivers should be written to emit <span class="code">None</span> if a data value is bad (perhaps
      