How to display two ThingSpeak dashboard channel widgets, one from actual data input, and the other calculated.

If I write data representing Fahrenheit temperature from my remote Raspberry Pi to my ThingSpeak channel “xxxxxx”, then I can select a widget from my ThingSpeak channel menu to represent the Fahrenheit temperature via round gage, square info box, or chart, etc. How can I add three addition widgets representing a “calculated” Celcius temperature in same channel display? And, the Fahrenheit temperature field will update every 15 to 40 seconds as that rate was chosen on Raspberry Pi so as not to exceed the 15 second limitation of ThingSpeak channel accepting the remote write. I would want the Celcius widgets to update at same time frame. My best guess so far is to us Matlab analysis to read and calculate then write, but to a different channel, not the same channel. And that calculation can only be accomplished every 5 minutes via time control. That’s the minimum time allowed. That is not acceptable. Too slow. In each widget’s setup are multiple user choice blocks allowing for ticks, labels, spans, and colors, etc, etc. Why is there no block for a simple math manipulation on a field before displaying it? Other IoT cloud services offer that feature. Why not ThingSpeak? Perhaps I am missing something. Let me know.