Вставлять туда, где вы желате видеть калькулятор.

код:

<!-- head start here -->

<style type="text/css">
<!--
body {font-family: helvetica}
p {font-size: 12pt}
.red {color: red}
.blue {color: blue}
-->
</style>

<script language="javascript">
<!-- original:  evsikoff_andrey -->
<!-- web site:  Зарегься чтобы увидеть ссылкиhttp://gsmevsikov.mybb.ru/ -->

<!-- begin
var memory = 0;
var number1 = "";
var number2 = "";
var newnumber = "blank";
var opvalue = "";

function display(displaynumber) {
document.calculator.answer.value = displaynumber;
}

function memoryclear() {
memory = 0;
document.calculator.mem.value = "";
}

function memoryrecall(answer) {
if(newnumber != "blank") {
number2 += answer;
} else {
number1 = answer;
}
newnumber = "blank";
display(answer);
}

function memorysubtract(answer) {
memory = memory - eval(answer);
}

function memoryadd(answer) {
memory = memory + eval(answer);
document.calculator.mem.value = " m ";
newnumber = "blank";
}

function clearcalc() {
number1 = "";
number2 = "";
newnumber = "blank";
display("");
}

function backspace(answer) {
answerlength = answer.length;
answer = answer.substring(0, answerlength - 1);
if (number2 != "") {
number2 = answer.tostring();
display(number2);
} else {
number1 = answer.tostring();
display(number1);
   }
}

function cecalc() {
number2 = "";
newnumber = "yes";
display("");
}

function checknumber(answer) {
if(answer == ".") {
number = document.calculator.answer.value;
if(number.indexof(".") != -1) {
answer = "";
   }
}
if(newnumber == "yes") {
number2 += answer;
display(number2);
}
else {
if(newnumber == "blank") {
number1 = answer;
number2 = "";
newnumber = "no";
}
else {
number1 += answer;
}
display(number1);
   }
}
function addbutton(x) {
if(x == 1) equalbutton();
if(number2 != "") {
number1 = parsefloat(number1) + parsefloat(number2);
}
newnumber = "yes";
opvalue = '+';
display(number1);
}
function subbutton(x) {
if(x == 1) equalbutton();
if(number2 != "") {
number1 = parsefloat(number1) - parsefloat(number2);
}
newnumber = "yes";
opvalue = '-';
display(number1);
}
function multbutton(x) {
if(x == 1) equalbutton();
if(number2 != "") {
number1 = parsefloat(number1) * parsefloat(number2);
}
newnumber = "yes";
opvalue = '*';
display(number1);
}
function divbutton(x) {
if(x == 1) equalbutton();
if(number2 != "") {
number1 = parsefloat(number1) / parsefloat(number2);
}
newnumber = "yes";
opvalue = '/';
display(number1);
}
function sqrtbutton() {
number1 = math.sqrt(number1);
newnumber = "blank";
display(number1);
}
function percentbutton() {
if(newnumber != "blank") {
number2 *= .01;
newnumber = "blank";
display(number2);
   }
}
function recipbutton() {
number1 = 1/number1;
newnumber = "blank";
display(number1);
}
function negatebutton() {
number1 = parsefloat(-number1);
newnumber = "no";
display(number1);
}
function equalbutton() {
if(opvalue == '+') addbutton(0);
if(opvalue == '-') subbutton(0);
if(opvalue == '*') multbutton(0);
if(opvalue == '/') divbutton(0);
number2 = "";
opvalue = "";
}
//  end -->
</script>

<!-- head end here -->

</head>
<body bgcolor="#ededed" text="#000000" link="#000000" topmargin="0" leftmargin="0">
<center>

<!-- body start here -->

<form name="calculator">
<table bgcolor="#aaaaaa" width=220>
<tr><td>
<table bgcolor="#cccccc" border=1>
<tr><td>
<table border=0 cellpadding=0>
<tr><td bgcolor="#000080"><b style="color:white">calculator</b></td></tr>
<tr><td>
<table width="100%" border=0>
<tr><td colspan=6><input type="text" name="answer" size=30 maxlength=30 onchange="checknumber(this.value)"></td></tr>
<tr><td colspan=6>
<table border=0 cellpadding=0>
<tr><td>
<input type="text" name="mem" size=3 maxlength=3> <input type="button" name="backspace" class="red" value="backspace" onclick="backspace(document.calculator.answer.value); return false;"> <input type="button" name="ce" class="red" value=" ce " onclick="cecalc(); return false;"> <input type="reset" name="c" class="red" value="  c  " onclick="clearcalc(); return false;">
</td></tr>
</table>
</td></tr>
<tr><td><input type="button" name="mc" class="red" value=" mc " onclick="memoryclear(); return false;"></td>
<td><input type="button" name="calc7" class="blue" value="  7  " onclick="checknumber('7'); return false;"></td>
<td><input type="button" name="calc8" class="blue" value="  8  " onclick="checknumber('8'); return false;"></td>
<td><input type="button" name="calc9" class="blue" value="  9  " onclick="checknumber('9'); return false;"></td>
<td><input type="button" name="divide" class="red" value="  /  " onclick="divbutton(1); return false;"></td>
<td><input type="button" name="sqrt" class="blue" value="sqrt" onclick="sqrtbutton(); return false;"></td></tr>
<tr><td><input type="button" name="mr" class="red" value=" mr " onclick="memoryrecall(memory); return false;"></td>
<td><input type="button" name="calc4" class="blue" value="  4  " onclick="checknumber('4'); return false;"></td>
<td><input type="button" name="calc5" class="blue" value="  5  " onclick="checknumber('5'); return false;"></td>
<td><input type="button" name="calc6" class="blue" value="  6  " onclick="checknumber('6'); return false;"></td>
<td><input type="button" name="multiply" class="red" value="  *  " onclick="multbutton(1); return false;"></td>
<td><input type="button" name="percent" class="blue" value=" %  " onclick="percentbutton(); return false;"></td></tr>
<tr><td><input type="button" name="ms" class="red" value=" ms " onclick="memorysubtract(document.calculator.answer.value); return false;"></td>
<td><input type="button" name="calc1" class="blue" value="  1  " onclick="checknumber('1'); return false;"></td>
<td><input type="button" name="calc2" class="blue" value="  2  " onclick="checknumber('2'); return false;"></td>
<td><input type="button" name="calc3" class="blue" value="  3  " onclick="checknumber('3'); return false;"></td>
<td><input type="button" name="minus" class="red" value="  -  " onclick="subbutton(1); return false;"></td>
<td><input type="button" name="recip" class="blue" value="1/x " onclick="recipbutton(); return false;"></td></tr>
<tr><td><input type="button" name="mplus" class="red" value=" m+  " onclick="memoryadd(document.calculator.answer.value); return false;"></td>
<td><input type="button" name="calc0" class="blue" value="  0  " onclick="checknumber('0'); return false;"></td>
<td><input type="button" name="negate" class="blue" value="+/- " onclick="negatebutton(); return false;"></td>
<td><input type="button" name="dot" class="blue" value="  .   " onclick="checknumber('.'); return false;"></td>
<td><input type="button" name="plus" class="red" value=" +  " onclick="addbutton(1); return false;"></td>
<td><input type="button" name="equal" class="red" value="  =   " onclick="equalbutton(); return false;"></td>
</tr>
</table>
</td></tr>
</table>
</td></tr>
</table>
</td></tr>
</table>
</form>

<!-- body end here -->