//Rename your Custom Field...
//Replace Your Custom Field with "custom_pessi_salary"
//Replace Custom Field wiht "custom_percentage_of_pessi_contribution"
//Replace Custom Field wiht "custom_pessi_6_pct_by_employer_"

frappe.ui.form.on('Employee', {
custom_pessi_salary: function(frm) {
calculate_pessi_6_pct_by_employer(frm);
},
custom_percentage_of_pessi_contribution: function(frm) {
calculate_pessi_6_pct_by_employer(frm);
}
});

function calculate_pessi_6_pct_by_employer(frm) {
var pessi_salary = frm.doc.custom_pessi_salary;
var pessi_contribution_percentage = frm.doc.custom_percentage_of_pessi_contribution;

if (pessi_salary && pessi_contribution_percentage) {
var pessi_6_pct_by_employer = (pessi_salary * (pessi_contribution_percentage / 100)).toFixed(2);
frm.set_value('custom_pessi_6_pct_by_employer_', pessi_6_pct_by_employer);
}
}