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 		</address>
 	</section>
 	<section>
+		<p>
+			In <strong>artificial-intelligence</strong>, you can end up dealing with all sorts of data.
+			For example —
+		</p>
+		<ul>
+			<li>maybe you are working with <em>photos</em> of people's faces;</li>
+			<li>maybe you are creating a list of <em>city names</em> of cities in the Near East;</li>
+			<li>maybe you have a list of <em>blood types</em> for all the patients that have visited the hospital;</li>
+
+			<li>maybe you are working with hospital patient data about how severe their pain was — ex: "<em>no pain</em>", "<em>mild pain</em>" , "<em>moderate pain</em>", "<em>it hurts bad</em>", and "<em><abbr title="oh my fucking! god">OMF!G</abbr>, this is the worst pain I have ever felt!</em>";</li>
+			<li>maybe you are looking at student <em>test scores</em>, graded oon a curve;</li>
+			<li>maybe you are recording the <em>birth order</em> (i.e., 1st child, 2nd child, 3rd child, etc) of all the people who work in a company;</li>
+
+			<li>maybe you are have <em>temperature<.em> records in °C (degree celsius);</li>
+			<li>maybe you are looking at the year every customer of a company was born;</li>
+
+			<li>maybe you are recording the <em>heights</em> of all the children in an elementary school;</li>
+			<li>maybe you are collecting the prices of houses in the city of Isfahan;</li>
+			<li>maybe you are are looking the number of photo each person takes every day on their mobile-phone;</li>
+
+			<li>etc etc etc.</li>
+		</ul>
+	</section>
+	<section>
+		<h2>Some Differences</h2>
+		<p>
+			Some of these data are very different than each other.
+		</p>
+		<p>
+			For example — if the price of one house is $1,000,000 and the price of another house is $500,000, then I can say the price of the first house is 2× (two times) bigger than the first.
+			(Since $1,000,000 = 2 × $500,000.)
+		</p>
+		<p>
+			But it is nonsense to say — <em>2 × type O+ blood</em>.
+			There is no concept of multiplying blood types.
+		</p>
+		<p>
+			The same is true for city names.
+			It is nonsense to say — <em>5 × the city of Vancouver</em>.
+		</p>
+	</section>
+	<section>
+		<h2>Types of Data</h2>
+		<p>
+			The <strong>levels of measurement</strong> are a way of understanding these <em>different types of data</em>.
+		</p>
 		<p>
 			The <strong>levels of measurement</strong> are a way of categorizing a <ziba-link>data</ziba-link> as one of four different categories:
 		</p>