Implementing a class

[paprica]

I'm trying to make a class that will help me calculating the delta time in my game.

dt.h:

#include <ctime>

class dt
{
public:
	void SetMaxFPS(int num);
	void UpdateCurrentTicks();
	void UpdateLastTicks();
	long GetDeltaTime();
	int GetFPS();
	int GetMaxFPS();
	bool UpdateNeeded();

private:
	long GetTicks();
	int max_fps;
	int current_ticks;
	int last_ticks;
};

dt.cpp:

#include "dt.h"

void dt::SetMaxFPS(int i)
{
	max_fps = i;
}

void dt::UpdateCurrentTicks()
{
	current_ticks = GetTicks();
}

void dt::UpdateLastTicks()
{
	last_ticks = current_ticks;
}

long dt::GetTicks()
{
	return clock();
}

long dt::GetDeltaTime()
{
	return current_ticks - last_ticks;
}

int dt::GetFPS()
{
	return (current_ticks - last_ticks) * 1000;
}

int dt::GetMaxFPS()
{
	return max_fps;
}

bool dt::UpdateNeeded()
{
	if(current_ticks > last_ticks + max_fps/1000)
		return true;
	return false;
}

main.cpp:

#include "dt.h"

int main(int argc, char* argv[])
{
	dt::SetMaxFPS(100);
}

And I get the next error:

error C2352: 'dt::SetMaxFPS' : illegal call of non-static member function

What am I doing wrong?