Use of the time mode on the axis

#include <time.h>

timeonaxis()
{
// This macro illustrates the use of the time mode on the axis
// with different time intervals and time formats. It's result can
// be seen  here 
// Through all this script, the time is expressed in UTC. some
// information about this format (and others like GPS) may be found at
//  http://tycho.usno.navy.mil/systime.html 
//  or
//  http://www.topology.org/sci/time.html 

   gROOT->Reset();

// The start time is : almost NOW (the time at which the script is executed)
// actualy, the nearest preceeding hour beginning.
// The time is in general expressed in UTC time with the C time() function
// This will obviously most of the time not be the time displayed on your watch
// since it is universal time. See the C time functions for converting this time
// into more useful structures.
   time_t script_time;
   script_time = time(0);
   script_time = 3600*(int)(script_time/3600);

// The time offset is the one that will be used by all graphs.
// If one changes it, it will be changed even on the graphs already defined
   gStyle->SetTimeOffset(script_time);

   ct = new TCanvas("ct","Time on axis",10,10,700,900);
   ct->Divide(1,3);
   ct->SetFillColor(28);

   int i;

//======= Build a signal : noisy damped sine ======
//        Time interval : 30 minutes

   gStyle->SetTitleH(0.08);
   float noise;
   ht = new TH1F("ht","Love at first sight",3000,0.,2000.);
   for (i=1;i<3000;i++) {
      noise = gRandom->Gaus(0,120);
      if (i>700) {
         noise += 1000*sin((i-700)*6.28/30)*exp((double)(700-i)/300);
      }
      ht->SetBinContent(i,noise);
   }
   ct->cd(1);
   ct_1->SetFillColor(41);
   ct_1->SetFrameFillColor(33);
   ht->SetLineColor(2);
   ht->GetXaxis()->SetLabelSize(0.05);
   ht->Draw();
// Sets time on the X axis
// The time used is the one set as time offset added to the value
// of the axis. This is converted into day/month/year hour:min:sec and
// a reasonnable tick interval value is chosen.
   ht->GetXaxis()->SetTimeDisplay(1);

//======= Build a simple graph beginning at a different time ======
//        Time interval : 5 seconds

   float x[100], t[100];
   for (i=0;i<100;i++) {
      x[i] = sin(i*4*3.1415926/50)*exp(-(double)i/20);
      t[i] = 6000+(double)i/20;
   }
   gt = new TGraph(100,t,x);
   gt->SetTitle("Politics");
   ct->cd(2);
   ct_2->SetFillColor(41);
   ct_2->SetFrameFillColor(33);
   gt->SetFillColor(19);
   gt->SetLineColor(5);
   gt->SetLineWidth(2);
   gt->Draw("AL");
   gt->GetXaxis()->SetLabelSize(0.05);
// Sets time on the X axis
   gt->GetXaxis()->SetTimeDisplay(1);
   gPad->Modified();

//======= Build a second simple graph for a very long time interval ======
//        Time interval : a few years

   float x2[10], t2[10];
   for (i=0;i<10;i++) {
      x2[i] = gRandom->Gaus(500,100)*i;
      t2[i] = i*365*86400;
   }
   gt2 = new TGraph(10,t2,x2);
   gt2->SetTitle("Number of monkeys on the moon");
   ct->cd(3);
   ct_3->SetFillColor(41);
   ct_3->SetFrameFillColor(33);
   gt2->SetFillColor(19);
   gt2->SetMarkerColor(4);
   gt2->SetMarkerStyle(29);
   gt2->SetMarkerSize(1.3);
   gt2->Draw("AP");
   gt2->GetXaxis()->SetLabelSize(0.05);
// Sets time on the X axis
   gt2->GetXaxis()->SetTimeDisplay(1);
//
// One can choose a different time format than the one chosen by default
// The time format is the same as the one of the C strftime() function
// It's a string containing the following formats :
//    for date :
//      %a abbreviated weekday name
//      %b abbreviated month name
//      %d day of the month (01-31)
//      %m month (01-12)
//      %y year without century
//      %Y year with century
//
//    for time :
//      %H hour (24-hour clock)
//      %I hour (12-hour clock)
//      %p local equivalent of AM or PM
//      %M minute (00-59)
//      %S seconds (00-61)
//      %% %
// The other characters are output as is.

   gt2->GetXaxis()->SetTimeFormat("y. %Y");
   gPad->Modified();
   
}