Phoebus Increased Slider Sensitivity?

["Leblanc, Gregory via Tech-talk" <tech-talk at aps.anl.gov>]

Hi,

I'm still sorting out the best way to control the magnets that we use to steer the particle beam through our beamlines.  I like the slider control because it mimics our current operation, and it feels intuitive when tuning beam.  Our existing control software allows operators to drag slider to a desired current for setting the current to the coarsest value.  The controls also have buttons that allow the user to select progressively finer controls allowing very precise tuning of the magnet parameters.  The "FINE" button affects the controls operation in 2 ways.  First, it adjusts the step size that the current moves when the operator single-clicks within the slider.  On the 0 to 50 slider, it moves 0.625 per click in coarse, 0.15 in medium, 0.04 in fine, 0.01 in extra fine, and 0.0025 in super fine.  Second, it adjusts the speed which the slider moves when the mouse is dragged within the slider area.  That is, the mouse position is de-coupled from the slider indicator on all the scales below coarse.  The operator might drag the cursor 50mm on the screen, but the slider indicator might only move 1 mm.  

I don't think there is a way to accomplish this exact behavior using Phoebus, which is OK if I can find another solution.

My first attempt was to make the limits of the scaled slider dynamic, and to have them pull their value from another element in the HMI, or from another PV.  Everything I tried had the slider back to the 0-100 scale, so I'm assuming that those can't be set on the fly.  The next thought I had was to add a choice button over the top of the slider and split the slider into 5-ish sub-sections.  Divide 250A down to 50A, then 50A down to 10A, and see if that gets me enough resolution to set the magnet.  I think this might work, but I'm not totally happy with it (plus I can't find documentation on how to use choice button to launch additional displays).  

TL; DR:  How do you control PVs that have a large overall range but need the ability to change by very fine increments?
     Greg 

--
Gregory Leblanc
Accelerator Engineer
Edwards Accelerator Lab - Ohio University
123 University Terrace
Athens, OH 45701 USA
leblanc at ohio.edu
M: (401) 52-OUAL1 or (401) 526-8251