Here’s an example of using BARSSINCE and SUMMATION. This may not be the only way to do this.

defparam drawonlastbaronly = true

//constants
daysBack = 1 // number of days back or maximum bars in chart!

// indicators
sma5 = average[5,0](close)
sma10 = average[10,0](close)

// crossover  condition
c = sma5 crosses over sma10

//  offset to last crossover
Clast = barssince(c,0)

// crossover bar
Xbar = (barindex-Clast)
//drawtext("#Xbar# crossovers",0,-60)anchor(top,xshift,yshift)


// threshold limit bar
Lbar = barindex -  (barssince(day<>day[1],daysBack-1)-1)
//drawtext("#Lbar# threshold limit bar",0,-60)anchor(top,xshift,yshift)



// drawing!

// if theres at least one crossover after threshold limit then display text
if Xbar > Lbar and cLast > -1 then

// draw last crossover line
drawVline(Xbar) coloured("red") style(dottedline,1) // crossover line

// draw text
bi = barindex // as a user variable
dif = Xbar-var  // difference between xover offset and threshold

drawtext("Threshold at bar #var# SMA5 last crossed over SMA10 at bar #Xbar# , #dif# bars from threshold ",0,40, dialog,standard,20)anchor(bottom,xshift,yshift)
drawtext("Also, last crossed over is  #Clast# bars back from current bar #bi# ",0,20, dialog,standard,20)anchor(bottom,xshift,yshift)
endif

// draw threshold limit line
var = barindex - (barindex - Lbar) // threshold bar
drawVline(var)   style(dottedline,1) // threshold line

// number of crossovers sine threhold bar
if barindex > var then
sum = summation[barindex-var](c)
drawtext("#sum# crossovers in range",0,-30)anchor(top,xshift,yshift)

Xover = summation[barindex-var](c) > 0
if Xover = 1 then
drawtext("#Xover# YES! ",0,-60)anchor(top,xshift,yshift)
else
drawtext("#Xover# NO! ",0,-60)anchor(top,xshift,yshift)
endif
endif



return sma5 coloured("red") as"sma5" ,sma10 coloured("lime") as"sma10",close style(dottedline,1)

Not sure where you going with this, with regards to original question.

BarsSince(condition,0) with’0′ gets the bar offset to last condition that was true, from the current bar..

Using ‘1’ gets the offset to the true condition prior to the last.

The saw tooth action is plotting the current continuous offset value,  since it is plotted every bar from on return line.

Additionally, the staggering level of the low of the saw tooth is because, when a new crossover happens,

the one being plotted stops being the prior one and the prior last one becomes the current prior one, and so on after each new crossover.

From your image I took it as you were highlighting the crossover points which is when you use ‘0’ in barsSince.

Regardless, of what value you put in BarsSince, each crossover will be highlighted other than  crossovers below n down to ‘0’

So the crossovers never change position with respects to the averages and the bars number there on, just the offset from the current barindex value.

Why did you only highlight 3 crossovers in your image?

This will return the number of occurrences withim the last N bars:

ONCE N = 5
MyMA5  = Average[5](close)
MyMA20 = Average[20](close)
return summation[N](MyMA5 crosses over MyMA20) style(histogram,1)

In your code, fast MA have to cross the 2 others at same barindex…

    ONCE N = 3
    MyMA5 = Average[5](close)
    MyMA10 = Average[10](close)
    MyMA20 = Average[20](close)

    A1 = summation[n](MyMA5 crosses over MyMA10)>0
    A2 = summation[n](MyMA5 crosses over MyMA20)>0

    R = A1 and A2

    return R