This Calculator model will take inputs from the Number 1 and Number 2 fields and when the user clicks on the relevant operator the result will be displayed in the Results field. For log10(), to radian, to degree, sin, cos, tan operations only require one input. Hence, the user is instructed to input the values to the 1st field only. First, before proceeding with the calculation, we need to obtain the values from the text boxes. For that we should include all the form elements inside a form. The result is directed to the same page. Therefore we will use the form action as $_SERVER['PHP_SELF'] and the method as post. Next, we can obtain the values in the text boxes. $_POST[' form_element_name '] will give you the value of the respective element. We can write the php code as follows (in the <head>) to obtain the value from Number 1 and Number 2 fields. <?php $num1=...