// at the click of a button = in a "button event callback":
allocate global_buffer[buf_len]; // the aggregate buffer spanning all channels
zero_fill(global_buffer); // the chart starts out showing a flat line at y=0
Chart1.AddSeries(global_buffer, buf_len, starting_freq, channel_width);
Chart1.adjust_axis_units_and_view_dimensions();
Ctrl::ProcessEvents();

for (each channel)
{
	tune_into(channel);
	sample_chunk_from_channel();
	calc_FFT_for_the_channel();
	// project per channel FFT results into the overview buffer
	memcpy(global_buffer+chnl_offset, channel_FFT_output, chnl_data_len); 
	Chart1.Refresh();    // tell the ScatterCtrl to update its output
	Ctrl::ProcessEvents();  // allow the GUI to actually carry out the updates pending :-)
}