多媒体定时器精度测试有关问题

多媒体定时器精度测试问题
我写了一个程序测试多媒体定时器的精读，但测试结果很不理想，只有当精读设置为250ms以上时才显示无误差。
下面是代码和测试结果
#include   "stdafx.h "

#include   <stdio.h>
#include   <windows.h>
#include   <Mmsystem.h>
#pragma   comment(lib, "winmm.lib ")     //安装多媒体定时器支持库,也可手动将winmm.lib添加到工程中。          
#include   <string>
#include   <vector>

#define   N   10    
using   namespace   std;
char   buffer[128]   =   {0};
vector   <string>   g_times;
void   CALLBACK   fun(UINT   uID,UINT   uMsg,DWORD   dwUser,DWORD   dw1,DWORD   dw2)
{
sprintf(buffer,   "Current   time:%lu\n ",timeGetTime());
string   szTime   =   buffer;
g_times.push_back(szTime);
}

int   _tmain(int   argc,   _TCHAR*   argv[])
{
UINT   wTimerRes;//=TIMER_ACCURACY;   //定义时间间隔
UINT   wAccuracy;   //定义分辨率
UINT   TimerID;   //定义定时器句柄
TIMECAPS   tc;
cin   > >   wTimerRes;
if(timeGetDevCaps(&tc,sizeof(TIMECAPS))==TIMERR_NOERROR)
{
wAccuracy=min(max(tc.wPeriodMin,wTimerRes),tc.wPeriodMax);   //判断分辨率是否在允许范围
timeBeginPeriod(wAccuracy);     //设置定时器分辨率
}

//设置定时器回调事件，回调函数形如fun
if((TimerID=timeSetEvent(wTimerRes,wAccuracy,(LPTIMECALLBACK)fun,0,TIME_PERIODIC))==0)
{
printf( "Can 't   count!\n ");
}

Sleep(N*wTimerRes);     //等待定时器线程执行N*TIMER_ACCURACY   ms

timeKillEvent(TimerID);
timeEndPeriod(wAccuracy);
for   (vector <string> ::iterator   ter   =   g_times.begin();   ter   !=   g_times.end();   ++ter)
{
string   sz   =   *ter;
cout   < <   sz;
}
}

结果：
10ms
Current   time:4844453
Current   time:4844468
Current   time:4844468
Current   time:4844484
Current   time:4844500
Current   time:4844500
Current   time:4844515
Current   time:4844531
Current   time:4844531
Current   time:4844546
Press   any   key   to   continue

50ms
Current   time:4861328
Current   time:4861374
Current   time:4861421
Current   time:4861468
Current   time:4861515
Current   time:4861578
Current   time:4861624
Current   time:4861671
Current   time:4861718
Current   time:4861765
Press   any   key   to   continue

100
Current   time:4875703
Current   time:4875796
Current   time:4875906
Current   time:4875999
Current   time:4876093
Current   time:4876203
Current   time:4876296
Current   time:4876406
Current   time:4876499
Current   time:4876593
Press   any   key   to   continue


200
Current   time:4888359
Current   time:4888562
Current   time:4888765
Current   time:4888968
Current   time:4889156
Current   time:4889359
Current   time:4889562
Current   time:4889765
Current   time:4889968
Current   time:4890156
Press   any   key   to   continue

250
Current   time:4903124
Current   time:4903374
Current   time:4903624