<form name="Form">
<input type="text"  style="width:155px;" name="Number">
<br>
<input type="button" value="1" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="2" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="3" 
onClick="document.Form.Number.value+=this.value"><br>
<input type="button" value="4" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="5" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="6" 
onClick="document.Form.Number.value+=this.value"><br>
<input type="button" value="7" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="8" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="9" 
onClick="document.Form.Number.value+=this.value"><br>
<input type="button" style="width:55px;" value="0" 
onClick="document.Form.Number.value+=this.value"><br>
<input type="button"  value="+" 
onClick="document.Form.Number.value+=this.value">
<input type="button"  value="-" 
onClick="document.Form.Number.value+=this.value">
<input type="button"  value="*" 
onClick="document.Form.Number.value+=this.value"><br>
<input type="button"  value="/" 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="." 
onClick="document.Form.Number.value+=this.value">
<input type="button" value="<<" onClick="Erase()"><br>
<input type="reset" style="width:55px;" value="C">
<br>
<input type="button" style="width:55px;" value="=" 
onClick="document.Form.Number.value=eval(document.Form.Number.value)">

</form>

<SCRIPT>
function Erase()
{
Length = document.Form.Number.value.length
document.Form.Number.value =
document.Form.Number.value.substring( 0 ,Length- 1 )
}
</SCRIPT>