The issue appears to be in the formatting of your mp_calcs_display() function. I modified the function to use the heredoc syntax for your html output, and was then able to activate the plugin successfully.
function mp_calcs_display() {
$output = <<<HTML
<form name="calsinput" action="" method="post" id="calsinput" ><h1> Process </h1>
<p> operation type always robot </p>
<br> <br>
Number of welds: <input type="number" name="numberofwelds" class="required digits" title="This field is required and must be a no." >
<br> <br>
Number of construction welds: <input type="number" name="numberofconwelds" class="required digits" title="This field is required and must be a no.">
<br> <br>
<h2> Outputs </h2>
<br> <br>
Robot in/out: <input type="text" name="robotinout" disabled>
<br> <br>
Weld time: <input type="text" name="weldtime" disabled>
<br> <br>
Controlling cycle: <input type="text" name="concycle" disabled>
<br> <br>
Total time(secs): <input type="text" name="totaltimesecs" disabled>
<br> <br> <br> <br>
<input type="submit" value="Calculate cycle time ">
</form>
<script type="text/javascript">
jQuery(document).ready(function($) {
$("#calsinput").validate();
});</script>
HTML;
return $output;
}
Full plugin file with above fix that was used for testing: https://gist.github.com/rachelbaker/ac13110e19321aed45ae