user3336: I am looking at the specs of a BenQ projector and trying to understand it's output frequency. 
On page 74 of the manual, there are specs for vertical, horizontal and "pixel" frequency. What does pixel frequency mean?

user-1: Pixel frequency, also known as dot clock is referring to the bandwidth of the projector's controller chip.
For a resolution a certain data rate is required to display all the data (not pixel frequency, see later) - it can be for example:
A resolution of 800x600 at 60 Hz would require:
800 x 600 x 3 (RGB) x 60 Hz/2 (interlaced frame rate) = 43 200 000 bytes per second

or divided on 1024^2 = 41.2 Mb/s, as data rate with full 8-bit color-depth.
To calculate the projector/monitor's bandwidth you will need accurate timing measurement available, but you can get close by using the vertical frequency and compensate for VBLANK (vertical blanking which is a sync feature) with about 5% and HBLANK with about 30%:
So with 800x600 resolution at 60 hz:  
800x1.3 x 600x1.05 x 60 = approx. 39 Mhz

The closer these two results get the better it is as that will tell that the projector/monitor is capable to handle the needed data rate to get full resolution, color depth as so forth.
The bandwidth becomes a factor when showing video in particular.

3336: <p>I am looking at the specs of a BenQ projector and trying to understand it's output frequency. </p>

<p>On page 74 of <a href="http://www.projectorcentral.com/pdf/projector_manual_5848.pdf" rel="nofollow">the manual</a>, there are specs for vertical, horizontal and "pixel" frequency. What does pixel frequency mean?</p>
 -1: <p>Pixel frequency, also known as <em>dot clock</em> is referring to the bandwidth of the projector's controller chip.</p>

<p>For a resolution a certain <em>data rate</em> is required to display all the data (not pixel frequency, see later) - it can be for example:</p>

<p>A resolution of 800x600 at 60 Hz would require:</p>

<pre><code>800 x 600 x 3 (RGB) x 60 Hz/2 (interlaced frame rate) = 43 200 000 bytes per second
</code></pre>

<p>or divided on 1024^2 = 41.2 Mb/s, as data rate with full 8-bit color-depth.</p>

<p>To calculate the projector/monitor's <em>bandwidth</em> you will need accurate timing measurement available, but you can get close by using the vertical frequency and compensate for VBLANK (vertical blanking which is a sync feature) with about 5% and HBLANK with about 30%:</p>

<p>So with 800x600 resolution at 60 hz:  </p>

<pre><code>800x1.3 x 600x1.05 x 60 = approx. 39 Mhz
</code></pre>

<p>The closer these two results get the better it is as that will tell that the projector/monitor is capable to handle the needed data rate to get full resolution, color depth as so forth.</p>

<p>The bandwidth becomes a factor when showing video in particular.</p>
