speed hud issue

have having trouble geting my text speed control hud to work right, it dosent update as it should, cant figure out what i did wrong

string text;
vector velocity;
string speed;

default
{
    state_entry()
    {
        llSetTimerEvent(.1);
    }
    timer()
    {
            velocity = llGetVel();
            speed = (string)llVecMag(velocity);
            speed = llGetSubString(speed, 0, llSubStringIndex(speed, ".") + 3);
            text += "  Speed: "  +speed+  " m/s";
            llSetText(text +"", <0.25, 0.25, 1.0>, 1.0);
    }
}

Since text is a global variable, " Speed: " +speed+ " m/s" is being appended to it each time through the timer loop. You want to just assign (=), not concatenate and assign (+=).

A few other things:

If you only want 3 digits after the decimal, it would be faster to use

llGetSubString( speed, 0, -4 )

Since a float cast to a string always includes 6 digits after the decimal.

In fact, the whole operation could be done in a single line inside timer, with no global variables necessary:

llSetText( llGetSubString( (string)llVecMag( llGetVel() ), 0, -4 ), <0.25, 0.25, 1.0>, 1.0 );

ok it works but now im trying to get it into messuing knots this is what i have, i get a error at the end of the line

speed = (integer)(llVecMag(velocity) * 1.94384449 + 0.5);

If speed is still a string variable, you need to cast to a string before assigning.