swift - provide simple method to get current speed (implementing speedometer) -

could please give me example how calculate current "speed", i'm working on first simple app ala speedometer?

i figure out use didupdatetolocation

also found need use formula speed = distance / duration

is right? how calculate duration?

the basic steps need go through this:

1. create cllocationmanager instance
2. assign delegate appropriate callback method
3. check see if "speed" set on cllocation in callback, if - there's speed

4. (optionally) if "speed" isn't set, try calculating distance between last update , current, divided difference in timestamps

   import corelocation  class locationdelegate: nsobject, cllocationmanagerdelegate {     var last:cllocation?     override init() {       super.init()     }     func processlocation(_ current:cllocation) {         guard last != nil else {             last = current             return         }         var speed = current.speed         if (speed > 0) {             print(speed) // or whatever         } else {             speed = last!.distance(from: current) / (current.timestamp.timeintervalsince(last!.timestamp))             print(speed)         }         last = current     }     func locationmanager(_ manager: cllocationmanager,                  didupdatelocations locations: [cllocation]) {         location in locations {             processlocation(location)         }     } }  var del = locationdelegate() var lm = cllocationmanager(); lm.delegate = del lm.startupdatinglocation()