This isn't possible with the constant sum question, so let's do it in a free format instead. Start by adding one variable to the free format for each item you want to appear in the \"constant sum.\" Each variable should be numeric with require response disabled.

The HTML should look something like this:


<table class=\"inner_table\">
\t<tbody>
\t\t<tr>
\t\t\t<td valign=\"top\" align=\"left\">
\t\t\t\t<table>
\t\t\t\t\t<tbody>
\t\t\t\t\t
\t\t\t\t\t\t<tr>
\t\t\t\t\t\t\t<td class=\"input_cell\">
\t\t\t\t\t\t\t\t<input name=\"[% QuestionName() %]_Variable1\" id=\"[% QuestionName() %]_Variable1\" class=\"numeric_input\" type=\"text\" size=\"3\">
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t\t<td class=\"option_cell\">
\t\t\t\t\t\t\t\t<div class=\"options\">
\t\t\t\t\t\t\t\t\t<label for=\"[% QuestionName() %]_Variable1\">
\t\t\t\t\t\t\t\t\t\tVARIABLE 1 LABEL
\t\t\t\t\t\t\t\t\t</label>
\t\t\t\t\t\t\t\t</div>
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t</tr>
\t\t\t\t\t\t
\t\t\t\t\t\t<tr>
\t\t\t\t\t\t\t<td class=\"input_cell\">
\t\t\t\t\t\t\t\t<input name=\"[% QuestionName() %]_Variable2\" id=\"[% QuestionName() %]_Variable2\" class=\"numeric_input\" type=\"text\" size=\"3\">
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t\t<td class=\"option_cell\">
\t\t\t\t\t\t\t\t<div class=\"options\">
\t\t\t\t\t\t\t\t\t<label for=\"[% QuestionName() %]_Variable2\">
\t\t\t\t\t\t\t\t\t\tVARIABLE 2 LABEL
\t\t\t\t\t\t\t\t\t</label>
\t\t\t\t\t\t\t\t</div>
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t</tr>
\t\t\t\t\t\t
\t\t\t\t\t\t<tr>
\t\t\t\t\t\t\t<td class=\"input_cell\">
\t\t\t\t\t\t\t\t<input name=\"[% QuestionName() %]_Variable3\" id=\"[% QuestionName() %]_Variable3\" class=\"numeric_input\" type=\"text\" size=\"3\">
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t\t<td class=\"option_cell\">
\t\t\t\t\t\t\t\t<div class=\"options\">
\t\t\t\t\t\t\t\t\t<label for=\"[% QuestionName() %]_Variable3\">
\t\t\t\t\t\t\t\t\t\tVARIABLE 3 LABEL
\t\t\t\t\t\t\t\t\t</label>
\t\t\t\t\t\t\t\t</div>
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t</tr>
\t\t\t\t\t\t
\t\t\t\t\t\t<tr>
\t\t\t\t\t\t\t<td class=\"input_cell\">
\t\t\t\t\t\t\t\t<input name=\"[% QuestionName() %]_total\" id=\"[% QuestionName() %]_total\" class=\"numeric_input total\" type=\"text\" size=\"3\">
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t\t<td class=\"option_cell\">
\t\t\t\t\t\t\t\t<div class=\"options\">
\t\t\t\t\t\t\t\t\t<label for=\"[% QuestionName() %]_total\">
\t\t\t\t\t\t\t\t\t\tTOTAL LABEL
\t\t\t\t\t\t\t\t\t</label>
\t\t\t\t\t\t\t\t</div>
\t\t\t\t\t\t\t</td>
\t\t\t\t\t\t</tr>
\t\t\t\t\t\t
\t\t\t\t\t</tbody>
\t\t\t\t</table>
\t\t\t</td>
\t\t</tr>
\t</tbody>
</table>

<style>
#[% QuestionName() %]_total {
\tbackground-color: #c0c0c0;
}
</style>

<script>
$(document).on('keyup', '#[% QuestionName() %]_div .numeric_input', function(){
\tvar sum = 0;
\t$('#[% QuestionName() %]_div .numeric_input:not(.total)').each(function(){
\t\tsum += parseInt($(this).val()) || 0;
\t})
\t$('#[% QuestionName() %]_total').val(sum);
})
</script>

Note the three blocks in the code for _Variable1, _Variable2, and _Variable3. You'll need to copy-and-paste those blocks so that you have one for each variable. Then you can replace \"_VariableN\" with the name of your free format variable.

Finally, you need custom JavaScript verification.

Verification for requiring the total be greater than 100:

[js]
var sum = 0;
$('#[% QuestionName() %]_div .numeric_input:not(.total)').each(function(){
\tsum += parseInt($(this).val()) || 0;
})

if (sum <= 100) {
\tstrErrorMessage = 'ERROR TEXT';
}
[/js]

Verification for requiring the total be less than 100:

[js]
var sum = 0;
$('#[% QuestionName() %]_div .numeric_input:not(.total)').each(function(){
\tsum += parseInt($(this).val()) || 0;
})

if (sum >= 100) {
\tstrErrorMessage = 'ERROR TEXT';
}
[/js]

Verification for requiring the total not be 100:

[js]
var sum = 0;
$('#[% QuestionName() %]_div .numeric_input:not(.total)').each(function(){
\tsum += parseInt($(this).val()) || 0;
})

if (sum != 100) {
\tstrErrorMessage = 'ERROR TEXT';
}
[/js]

Please tell me if you have any problems getting this to work.

Constant Sum Question