There are many ways to fix the size of a PHP chart, and to make it monometric. A particularly simple way is to use tables and the embed command (choose appropriately width and height).  See the examples below.

SEE

<title>head_a</title>
<table cellpadding=0 cellspacing=0 align=center border=1  bordercolor=orange>
<tr>
<td>
<embed width="480" height="350" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
</tr>
</table>

  OR:

<title>head_a</title>
<table cellpadding=0 cellspacing=0 align=center border=1 bordercolor=orange width=480 height=350>
<tr>
<td>
<embed width=100% height=100% src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
</tr>
</table>

SEE

<title>head_b</title>
<table cellpadding=0 cellspacing=0 align=center border=0><tr>
<td>
<embed width="800" height="550" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
</tr>
</table>

SEE

<title>circle</title>
<table cellpadding=0 cellspacing=0 align=center border=0><tr>
<td>
<embed width="500" height="500" src="http://macosa.dima.unige.it/handbook/graph_php/circle.php">
</td>
</tr>
</table>

SEE

<title>example_1</title>
<table cellpadding=0 cellspacing=0 align=center width=100% border=0><tr>
<td>
<embed width="500" height="380" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
<td>
<embed width="600" height="270" src="http://macosa.dima.unige.it/handbook/graph_php/bacin.php">
</td>
</tr>
</table>

SEE

<title>example_1</title>
<table cellpadding=0 cellspacing=0 align=center width=100% border=1 bordercolor=red><tr>
<td>
<embed width="500" height="380" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
<td>
<embed width="600" height="270" src="http://macosa.dima.unige.it/handbook/graph_php/bacin.php">
</td>
</tr>
</table>

SEE

<title>example_1</title>
<table cellpadding=0 cellspacing=0 align=center width=100% border=0><tr>
<td align=center>
<embed width="450" height="340" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
<td align=center>
<embed width="600" height="270" src="http://macosa.dima.unige.it/handbook/graph_php/bacin.php">
</td>
</tr>
</table>
<table cellpadding=0 cellspacing=0 align=center width=100% border=0><tr>
<td align=center>
<embed width="300" height="300" src="http://macosa.dima.unige.it/handbook/graph_php/spiral.php">
</td>
<td align=center>
<embed width="450" height="300" src="http://macosa.dima.unige.it/handbook/graph_php/ellips.php">
</td>
</tr>
</table>

SEE

<title>example_1</title>
<table cellpadding=0 cellspacing=0 align=center width=100% border=1><tr>
<td align=center>
<embed width="450" height="340" src="http://macosa.dima.unige.it/handbook/graph_php/head.php">
</td>
<td align=center>
<embed width="600" height="270" src="http://macosa.dima.unige.it/handbook/graph_php/bacin.php">
</td>
</tr>
<tr>
<td align=center>
<embed width="300" height="300" src="http://macosa.dima.unige.it/handbook/graph_php/spiral.php">
</td>
<td align=center>
<embed width="450" height="300" src="http://macosa.dima.unige.it/handbook/graph_php/ellips.php">
</td>
</tr>
</table>