How to write an interface but with different signatures

[Chris Katko]

I know that sounds stupid on the face of it. An interface 
shouldn't change. But consider this:

A frame timer and a clock timer(seconds) that re-use 
functionality from a parent class/interface.

```
class timerType
	{
	void start() = 0;
	void stop() = 0;
	void restart() = 0;
	void set(?) = 0; // ????
	}

class frameTimer : timerType
	{
         void set(int numFrames){}
	}
	
class clockTimer : timerType
	{
         void set(float numSeconds){}
	}

```

If we put both signatures in the top we're kind of polluting the 
interface. If we don't put them in the interface, then you can 
create a timer with no set() function.

None of this is super important on a practical level. There's 
going to probably be a total of two or three timer types. But as 
a learning exercise, I'm curious if there is a right/proper/best 
way to solve this conceptual problem.

And to be clear, frames and seconds are NOT directly 
interchangeable or convertible. If the game runs at 2 FPS for a 
moment, a 5 second timer is still 5 seconds (e.g. a countdown), 
but a frame timer of 2 (for an animation) is still going to be 2 
frames.