Selling a cloth in 20cm lengths with the user inputing the length in metres.  (Tested with 6.1.2)
This works with sections using "Quantity on Product page".
The following will allow a length to be input in a fractional number of metres (like 1.23 metres) 
and will round it up to the next 20cm.
The actual length ordered in metres and the number of 20cm units will be displayed in the Other Info Prompt.




Put the following code into Act_Primary.html (just above the </HEAD> tag).




<script language=JavaScript>
<!-- Support for Fractional Quantities - Norman Rouxel - rouxel@drillpine.biz
function formfield(fname){		// look through all forms 'till one containing field "fname"
  var df = document.forms;		// simplified version - only return object fname
  var i = df.length - 1;
  for ( var j = 0; j <= i; j++ )
    {
    var k = df[j].length - 1; 
    for ( var l = 0; l <= k; l++ )
      {
      if ( df[j].elements[l].name == (fname) ) 
        {
        return df[j].elements[l];
        }
      }
    }
  alert('Cannot find field ' + fname);  // shouldn't happen...
  return false;
}
function fixnum(prodref){
  var val = formfield('JV-' + prodref).value - 0;	// make a number
  if ( ( val <= 0 ) || isNaN(val) ) 
    {
    val = 1;					// silently set to 1 for bad input.
    }
  var intval = Math.ceil(val * 5); 		// number of 20cm units rounded up
  val = intval / 5;                		// round back to decimal value to nearest 20 cm
  formfield('Q_' + prodref).value = intval;  	// put integer value in Actinic's Quantity field
  formfield('JV-' + prodref).value = val;  	// put rounded value in Visible Quantity field
  // put values into Other Info field plus a unique hidden sequence number to avoid merging of quantities
  formfield('O_' + prodref).value = val + ' Metres - (' + intval + ' x 20cm Units) <!-- Code: ' + Date.parse(Date()) + ' -->';
  return true;
}

function handleEnter (field, event) {   // disable enter key for our fractional quantity fields.
		var keyCode = event.keyCode ? event.keyCode : event.which ? event.which : event.charCode;
		if (keyCode == 13) return false; 
		return true;
}  
// -->
</script> 










Save the following chunk of code as Cloth_ProductLine.html



<!-- Cloth_ProductLine HTML begin -->
<!-- Insert HTML for the top of the individual product -->
NETQUOTEVAR:INCLUDE Act_ProductSeparator.html
NETQUOTEVAR:ENDSEPARATOR
NETQUOTEVAR:PRODUCTFORMBEGIN
  <tr>
    <td rowspan="2" valign="TOP" align="CENTER"> NETQUOTEVAR:TEMPLATEBEGINXML NETQUOTEVAR:PRODUCTIMAGE </td>
    <td valign="TOP" align="LEFT" colspan="2">  
      <a name="NETQUOTEVAR:PRODUCTANCHOR"><span class="actregular"><b>NETQUOTEVAR:PRODUCTNAME</b></span></a>
      <span class="actxsmall">NETQUOTEVAR:PRODUCTREF <br>
      NETQUOTEVAR:PRODUCTDESCRIPTION&nbsp;NETQUOTEVAR:EXTINFOLINK</span>NETQUOTEVAR:EXTINFOBUTTON
      <br>
      <span class="actxsmall">NETQUOTEVAR:PRODUCTBEGINLINKNETQUOTEVAR:PRODUCTLINKTEXTNETQUOTEVAR:PRODUCTENDLINK
      NETQUOTEVAR:PRICEEXPLANATION </span><br>
      <b>NETQUOTEVAR:PRODUCTPRICE</b>
      <!-- <span class="actxsmall">NETQUOTEVAR:OTHERINFOPROMPT </span> -->
      <span class="actxsmall">NETQUOTEVAR:DATEPROMPT </span>
    </td>
  </tr>
  <tr>
    <td align="LEFT" colspan="2"><span class="actxsmall">
			NETQUOTEVAR:CARTERRORXML<!-- NETQUOTEVAR:PRODUCTQUANTITY-->
<input type=hidden name="Q_NETQUOTEVAR:PRODUCTREFERENCE" value="5">
<script language=JavaScript>
<!--
document.write('<input type=hidden name="O_NETQUOTEVAR:PRODUCTREFERENCE" value="1 Metres (5 x 20cm Units) <!-- Code: ' + Date.parse(Date()) + ' -->">');
// -->
</script>
Enter length in Metres (e.g. 1.2) <input type=text size=4 name="JV-NETQUOTEVAR:PRODUCTREFERENCE" value="1" autocomplete=off onkeypress="return handleEnter(this, event)" onchange="fixnum('NETQUOTEVAR:PRODUCTREFERENCE')">
<br>
			<Actinic:ACTIONS>NETQUOTEVAR:ADDTOCARTBUTTON</Actinic:ACTIONS>
		    </span>
	NETQUOTEVAR:TEMPLATEENDXML
       </td>
  </tr>
NETQUOTEVAR:PRODUCTFORMEND
NETQUOTEVAR:NEXT
<!-- Insert HTML for the bottom of the individual product -->
<!-- Cloth_ProductLine HTML end -->






Now we have to display the customised quantity prompt for these special products.

Edit ActinicOrder.pm (make a backup copy first) - use a text editor, not a word processor - e.g. www.editpadlite.com.

Search for the line (there is only 1 occurence):-


		$sHTML = "<INPUT TYPE=TEXT SIZE=\"35\" NAME=\"O_$nIndex\" VALUE=\"$sValue\" $sStyle>";


REPLACE it with the following fragment:-


                if ( $sValue =~ m/<!--/ )			# Norman patching for Cloth Sizes
			{
			$sValue =~ m/(\d+\.*\d*) (.*)/;     		# extract the number and informative string
			$sHTML = "<input type=text size=4 name=\"JV-$nIndex\" value=\"$1\" autocomplete=off style=\"text-align: right\" onkeypress=\"return handleEnter(this, event)\" onchange=\"fixnum('$nIndex')\"> $2" .
				 "<INPUT TYPE=hidden NAME=\"O_$nIndex\" VALUE=\"$sValue\">";
			}
		else
			{
			$sHTML = "<INPUT TYPE=TEXT SIZE=\"35\" NAME=\"O_$nIndex\" VALUE=\"$sValue\" $sStyle>";
			}					# End of Norman patching for Cloth Sizes



That fixes the Other Info Prompt so that it contains a qauntity field and some update code.


Now we have to make the Actinic Quantity field uneditable for these products.
Still in ActinicOrder.pm - Search for the line (there is only 1 occurence):-


		if ($$pProduct{"MIN_QUANTITY_ORDERABLE"} != $$pProduct{"MAX_QUANTITY_ORDERABLE"}	&& # The quantity might change


The following line should be:-


			 $bIncludeButtons)


REPLACE that line with:-


			 $bIncludeButtons && $CurrentItem{'INFO'} !~ /<!--/)				# Norman Patching for Cloth Sizes




Save and exit from editing ActinicOrder.pm


That's all patching finished.
  
Note that if you update Actinic to a new version or patch level then these patches 
to ActinicOrder.pm will be overwritten and you'll have to do them again.



Now in your product details:

Make sure your section is set to "Quantity on Product page".
Select Cloth_ProductLine.html as the product template.
Set the product price to be correct for 20cm of fabric.
Set the Other Info Prompt to be "Length"
Set the Price Prompt to be "Price per 20cm:".

Now when the customer enters a length it will be rounded to the next 20cm and the correct number 
of 20cm units will be added to the cart.
In addition the Other Info Prompt will be set to contain the actual number of metres of cloth 
ordered and number of 20cm units.