[Tim_Ethen]

My comments explain it pretty good. Please read this and do not just copy and paste it.

PHP Code:

#include <a_samp>
new Float:svx[MAX_PLAYERS]; // Holds Velocity X
new Float:svy[MAX_PLAYERS]; // Holds Velocity Y
new Float:svz[MAX_PLAYERS]; // Holds Velocity Z
new Float:s1[MAX_PLAYERS]; // This Is What Our Forumula Outputs
new s2[MAX_PLAYERS]; // This Is The Output When The Forumula's Ouput Is Round
new s3[MAX_PLAYERS][256]; // This Is The Text That Is Displayed To The User
new Text:sdisplay[MAX_PLAYERS]; // This Holds The Textdraw's ID
new stimer[MAX_PLAYERS]; // This Holds The Timer's ID (Used To Refresh Speed)
forward speedometer(playerid); // This Forwards The Timer To Our Function
public OnFilterScriptInit() { // This Is What Is Excuted When The FilterScript Starts
    print("                                       ");
    print("  -----------------------------------  ");
    print("                                       ");
    print("  Speedometer Filterscript Has Loaded  ");
    print("                                       ");
    print("  -----------------------------------  ");
    print("                                       ");
    return 1;
}
public OnFilterScriptExit() { // This Is What Is Excuted When The FilterScript Ends
    print("                                         ");
    print("  -------------------------------------  ");
    print("                                         ");
    print("  Speedometer Filterscript Has Unloaded  ");
    print("                                         ");
    print("  -------------------------------------  ");
    print("                                         ");
    return 1;
}
public OnPlayerConnect(playerid) {
    sdisplay[playerid] = TextDrawCreate(10.0,200.0," "); // This Creates Our Textdraw And Stores The Id In The Varible In Front
    TextDrawSetShadow(sdisplay[playerid],0); // This Removes Our Textdraw's Shadow ( Makes Easier To Read )
    TextDrawSetOutline(sdisplay[playerid],1); // This Adds A Black Outline To Our Textdraw ( Makes Easier To Read )
    TextDrawFont(sdisplay[playerid], 2); // This Changes Our Textdraw's Font ( I Think This Ones Makes It Easier To Read )
    TextDrawShowForPlayer(playerid,sdisplay[playerid]); // This Shows The User The Textdraw
    return 1;
}
public speedometer(playerid) {
    GetVehicleVelocity(GetPlayerVehicleID(playerid), svx[playerid], svy[playerid], svz[playerid]); // This Saves Our Velocitys To Our Varibles
    s1[playerid] = floatsqroot(((svx[playerid]*svx[playerid])+(svy[playerid]*svy[playerid]))+(svz[playerid]*svz[playerid]))*100; // This Is Our Forumula ( I Don't Know How It Works )
    s2[playerid] = floatround(s1[playerid],floatround_round); // This Rounds Our Output To The Nearest Whole Number
    format(s3[playerid],256,"%i MPH", s2[playerid]); // This Format Our Text Into What We See
    TextDrawSetString(sdisplay[playerid], s3[playerid]); // This Changes The Value Of Our Textdraw To What We Formatted
    return 1;
}
public OnPlayerStateChange(playerid, newstate, oldstate) { // This Is The Callback That Is Called When A Person Changes State ( ex States In_Vehicle, Dead, Passenger, Speculating... )
    KillTimer(stimer[playerid]); // This Stops Our Timer For When You Get Out Of Your Vehicle Your Speed Doesn't Keep Going
    TextDrawSetString(sdisplay[playerid], " "); // This Sets Our Textdraw To Blank And Freezes Because We Stop The Timer ^
    if(newstate == 2) stimer[playerid] = SetTimerEx("speedometer", 255, true, "i", playerid); // This Starts The Timer When The Player Changes His/Her State To Being The Driver
    else if(newstate == 3) stimer[playerid] = SetTimerEx("speedometer", 250, true, "i", playerid); // This Start The Timer When The Player Changes His/Her Start To Being The Passenger
    return 1;
}