<script type="text/javascript">
        // calculate gear inches and development
        function calculateGear() {
            var chainring = document.getElementById("chainring").value
            var cog = document.getElementById("cog").value
            document.getElementById("gear-inches-nominal").value = Math.round(chainring/cog*27*10)/10
            // document.getElementById("gear-inches-actual").value = Math.round(chainring/cog*26.27*10)/10
            document.getElementById("development").value = Math.round(chainring/cog*2.096*100)/100

            // calculate times from cadence
            if (document.getElementById("cadence").value>0){
                calculate1()
            }

            if (document.getElementById("mph2").value>0){
                calculate2()
            }

            if (document.getElementById("kph3").value>0){
                calculate3()
            }
        }

        // calculate mmss from seconds - expects a number, returns a string

        function secsToMmSs(seconds){
            minutes = Math.floor(seconds/60)
            seconds = Math.round((seconds%60)*100)/100
            if (seconds === 60) {
                seconds = 0
                minutes = minutes + 1
            }
            time = minutes + ":" + seconds
            if (seconds<10) {
                time = minutes + ":" + "0" + seconds
            }
            return time
        }

        // calculate 200m - 333m times
        function calculateShortTimes(metersPerSecond) {
            document.getElementById("m200").value = Math.round(200/metersPerSecond*100)/100
            document.getElementById("m250").value = Math.round(250/metersPerSecond*100)/100
            document.getElementById("m268").value = Math.round(268/metersPerSecond*100)/100
            document.getElementById("m333").value = Math.round(333.33/metersPerSecond*100)/100
        }

        // calculate 500m to 4000m times
        function calculateMultiLapTimes(metersPerSecond, startingLap) {
            document.getElementById("m500").value = Math.round(startingLap*100)/100 + Math.round((250/metersPerSecond)*100)/100
            document.getElementById("m750").value = Math.round(startingLap*100)/100 + Math.round((500/metersPerSecond)*100)/100

            // calculate times and convert to MM:SS
            seconds = Math.round(startingLap*100)/100 + 750/metersPerSecond
            document.getElementById("m1000").value = secsToMmSs(seconds)

            seconds = Math.round(startingLap*100)/100 + 1750/metersPerSecond
            document.getElementById("m2000").value = secsToMmSs(seconds)

            seconds = Math.round(startingLap*100)/100 + 2750/metersPerSecond
            document.getElementById("m3000").value = secsToMmSs(seconds)

            seconds = Math.round(startingLap*100)/100 + 3750/metersPerSecond
            document.getElementById("m4000").value = secsToMmSs(seconds)
        }



        // calculate times from cadence
        function calculate1() {
            var chainring = document.getElementById("chainring").value
            var cog = document.getElementById("cog").value
            var cadence = document.getElementById("cadence").value
            var metersPerSecond = cadence*chainring/cog*2.096/60

            document.getElementById("kph").value = Math.round((cadence*chainring/cog*2.096*60/1000)*10)/10

            var calculatedKph = document.getElementById("kph").value
            document.getElementById("mph").value = Math.round((calculatedKph/1.60934)*10)/10

            // clear other values
            document.getElementById("cadence2").value = null
            document.getElementById("mph2").value = null
            document.getElementById("kph2").value = null

            document.getElementById("cadence3").value = null
            document.getElementById("mph3").value = null
            document.getElementById("kph3").value = null

            //calculate times

            var startingLap = document.getElementById("startinglap").value
            calculateShortTimes(metersPerSecond)
            if (startingLap > 0){
                calculateMultiLapTimes(metersPerSecond, startingLap)
            }
        }

        // calculate times from mph
        function calculate2(){
            var speedMph = document.getElementById("mph2").value
            var speedKph = speedMph*1.60934
            var metersPerSecond = speedKph*1000/3600


            // write kph
            document.getElementById("kph2").value = Math.round(speedKph*100)/100

            // calculate cadence
            var chainring = document.getElementById("chainring").value
            var cog = document.getElementById("cog").value
            document.getElementById("cadence2").value = Math.round(speedKph*1000*cog/(chainring*2.096*60))

            // clear other values
            document.getElementById("cadence").value = null
            document.getElementById("mph").value = null
            document.getElementById("kph").value = null

            document.getElementById("cadence3").value = null
            document.getElementById("mph3").value = null
            document.getElementById("kph3").value = null


            //calculate times
            var startingLap = document.getElementById("startinglap").value
            calculateShortTimes(metersPerSecond)
            if (startingLap > 0){
                calculateMultiLapTimes(metersPerSecond, startingLap)
            }
        }



        // calculate times from kph
        function calculate3(){
            var speedKph = document.getElementById("kph3").value
            var metersPerSecond = speedKph*1000/3600
            var startingLap = document.getElementById("startinglap").value

            // calculate mph
            document.getElementById("mph3").value = Math.round(speedKph*.621371*100)/100

            // calculate cadence
            var chainring = document.getElementById("chainring").value
            var cog = document.getElementById("cog").value
            document.getElementById("cadence3").value = Math.round(speedKph*1000*cog/(chainring*2.096*60))


            // clear other values
            document.getElementById("cadence").value = null
            document.getElementById("mph").value = null
            document.getElementById("kph").value = null

            document.getElementById("cadence2").value = null
            document.getElementById("mph2").value = null
            document.getElementById("kph2").value = null

            // calculate times
            calculateShortTimes(metersPerSecond)
            if (startingLap > 0){
                calculateMultiLapTimes(metersPerSecond, startingLap)
            }
        }

        function startLapCalc() {
            var kph = document.getElementById("kph").value + document.getElementById("kph2").value + document.getElementById("kph3").value
            var mps = kph * 1000/3600
            var start = document.getElementById("startinglap").value

            if (mps > 0) {
                calculateMultiLapTimes(mps, start)
            }
        }


    </script>