I am working with samples and have my ruler, the main NowTime display and the time display on the left all set to Samples.
 
But whenever I want to set a marker it will only position it more or less around the Now cursor.
 
Markers appear to be time-based only and cannot be told to position themselves over a sample.
I deduce that from the dialog which has an edit box where I can enter a position manually - but only to a particular time.
 
Is there any way to change this? I want to mark where the attack of a guitar chord starts with a view to selecting one of a number of such attack points later. 
 
 
 

I believe you are correct. I had asked this question a while back and Brundlefly confirmed there was no was to place a marker with sample accuracy. It does land within a dozen samples or so, so is unclear that in your situation if that is not suitable.
 
In my case, I had literally edited a sample to disprove an assertion that a single sample modification is audible. Turned out that single sample alteration made the audio engines of a DAW insert white noise for several hundred samples on either side (which is audible). As I went back into the original file to find the edit, the marker I put in would only drop about 7 samples away which was close enough to find it later.

Thanks for responding.
 
Funny, because the clip snipping dialog allows you to choose the measure type you want to use. And looping positions its flags on samples, from what I can see.
 
Anyway, not a major problem. Just odd.

True... it doesn't affect actual clip work, only marker positions. Since we rely on splitting at zero crossings, that would cause issues.
 
Have you actually tried your chords in practice? I have dropped markers willy-nilly in songs before and jumped between them without issues. Is it more that you are trying to use this for composition?

I've always found 1 ms to be sufficient resolution for markers. OTOH hand being able to trim clips and loops for sample accuracy, which SONAR can do, was a big deal back in the day before stretching became commonplace. People using loops expected trimming to be sample accurate to the stated tempo.