How do I use findvalue /RMD for x-value

I assume that by xy wave you mean a 2D wave containing both height and time values (otherwise there is no need for /RMD).

You would use findvalue/RMD to search the dimension (row or column) of the 2D wave that contains the time data, then take the height from the corresponding row/column.

Yes, a 2D wave. What would be the syntax of /RMD ?

I've tried a number of combinations and am not finding value.  Also used /T = deltaX

for example 

tolerance =deltaX(myLineFitdata)

findvalue /V=(searchTime) /RMD=[0,*][0,*] /T=(tolerance)  myLineFitdata

if column 0 contains time and column 1 height, then something like

I still can't get it to work  - here is my code and debugger details

searchTime = 3724010668.16396 (Variable)  

I skipped the /T flag in my post, but you probably need to reinsert that.

Looks like your screenshot is a 1D fit wave, not a 2D wave. Then you simply use the wave scaling:

print LineFit_Lat(searchTime)

Note the curved parentheses.

Thanks Tony - that works - and so easy. 

 I obviously need to learn my dimensions :-)

Is this method documented?  Does it extrapolate?

The automatically generated output from curve fitting is waveform. Execute:

DisplayHelpTopic "The Waveform Model of Data"

so x-values are computed rather than stored.

Igor interpolates linearly, but has no way of knowing how to extrapolate.

Mike- you have done so much with Igor that is so sophisticated, that I hesitate to suggest it... The confusion over wave scaling, waveform data vs multidimensional vs XY data suggests that you may benefit from a quick review of the Getting Started help. I find that every few years even I benefit from reviewing Getting Started, and I wrote a lot of what's in there!

> may benefit from a quick review of the Getting Started help.

On every level of IP expertise consulting the documentation is required. I consult the documentation really often as well.

I do as well and my insomnia is now a thing of the past.

More seriously, I do browse it to get a better understanding of what can be done when the need arises.

Andy

John - if I have managed to do anthing sothisticated it is because Igor allows me to do it - and there is the great group of experts to advise.  I have been using Igor for a good number of years; when I was earning a living it was the tool I used for quality  graphs. I used FORTRAN for number crunching - but, lathough I love programming with IGOR I am not a programmer.   I retired some twelve years ago and it was not until about six or seven years ago when I became interested in Radio meteor physics and started collecting masses of data that I came back to it.  The data I collect is time based parameters but with irregular time intervals so all my wave were just time or frequency or signal level etc and no real possibility of using the waveform data.  As my needs developed I found through this group that some things are much easier to do with wavemodel.

So John, you are absolutely right I should and shall go and look at the Getting started help again after many years. 

But I will still have plenty more question for the Forum.

Thanks again group!

Thanks so much, Mike! I find that if I take a month off of programming I get rusty.