Hi,
In the template.php
Find:
<span class="bmi-calculator-system-imperial">
<input type="radio" class="bmi-calculator-system-radio" value="imperial" checked="checked"/> Imperial
</span>
<span class="bmi-calculator-system-metric">
<input type="radio" class="bmi-calculator-system-radio" value="metric"/> Metric
</span>
and change it to:
<span class="bmi-calculator-system-imperial">
<input type="radio" class="bmi-calculator-system-radio" value="imperial"/> Imperial
</span>
<span class="bmi-calculator-system-metric">
<input type="radio" class="bmi-calculator-system-radio" value="metric" checked="checked"/> Metric
</span>