Assigning an equation as a variable

Question

I am compiling a calculator where many slider parameters are used to define a value, where the defined value may then be reused to define another value. I am unable able to, or at least been unsuccessful in assigning these values as variables.

I want my coding to be able to refer to a variable (where the variable is an equation) in the sense, however the equation is defined by slider parameters and doesn't initially contain values.

An example of this is a three-step formulation, where the first equation requires parameters defined through sliders, a second equation requires the value from the first equation and another slider parameter, then a third equation requires the value from the second equation and another slider; variables A, C and F are defined from individual sliders like this:

Row[{"Magnification: ", F/C}],
Row[{"Exit Pupil: ", A/(F/C)}],
Row[{"Longest Useful FOV: ", F/(A/(F/C))}],

{{A, 130, "Aperature: "}, 60, 508, 1, Appearance -> "Labeled"},
{{F, 650, "Focal Length: "}, 480, 4064, 1, Appearance -> "Labeled"},
{{C, 32, "Occular Focal Length: "}, 1, 110, 1, Appearance -> "Labeled"},

An easier way to express this would be and how I would like it to display is like this:

Row[{"Magnification: ", F/C = M}],
Row[{"Exit Pupil: ", A/M = E}],
Row[{"Longest Useful FOV: ", F/E}],

I am unable to find a way where this is achieved, the calculator hosts several instances like this however some require the value from another equation without a parameter set from a slider. Some equations are reused multiple times, due to the equations being used there are inconsistencies with formulation until some sliders have changed their values.

I have a working example with complete code if required to see the depth of the formulation, however none of the equations require more than a three-step formulation.

Edit - Full Code

$S1 = Bold;
$S2 = Orange;

Manipulate[
 N@Grid[{
  {Style["Focal Ratio: ", $S1], Style[FL/AD, $S2]},
  {Style["Dawes Limit: ", $S1], Style[115.824/AD, $S2]},
  {Style["Rayleigh Limit: ", $S1], Style[139.7/AD, $S2]},
  {Style["Gathering Power: ", $S1], Style[(AD/OP)^2, $S2]},
  {Style["Magnification: ", $S1], Style[N[FL/OL, 4], $S2]},
  {Style["Min Magnification: ", $S1], Style[N[AD/OP, 4], $S2]},
  {Style["Exit Pupil: ", $S1], Style[N[AD/(FL/OL), 3], $S2]},
  {Style["True FOV (No F/Stop): ", $S1], Style[N[OF/(FL/OL), 3], $S2]},
  {Style["True FOV (F/Stop): ", $S1], Style[N[(.0957*OL*OF*N[Pi]/180)/FL 57.3, 3], $S2]},
  {Style["Max FOV: ", $S1], Style[N[31.7 180/N[Pi]/FL, 3], $S2]},
  {Style["Longest Useful FOV: ", $S1], Style[N[FL/(AD/(FL/OL)), 5], $S2]},
  {Style["Magnitude Limit: ", $S1], Style[NumberForm[7.5 + 5 Log10[AD/10], 4], $S2]},
  {Style["Ocular Field Stop: ", $S1], Style[N[.0957*OL*OF*N[Pi]/180, 4], $S2]}
 }],
{{AD, 130, "Aperature: "}, 60, 508, 1, Appearance -> "Labeled"},
{{FL, 650, "Focal Length: "}, 480, 4064, 1, Appearance -> "Labeled"},
{{OL, 32, "Occular Focal Length: "}, 1, 110, 1, Appearance -> "Labeled"},
{{OF, 52, "Occular FOV: "}, 40, 72, 1, Appearance -> "Labeled"},
{{OP, 7, "Observer's Pupil: "}, 4, 9, 1, Appearance -> "Labeled"}
]

I reworked the layout to a Grid, I will have to adjust the decimals still. There are no more compiling errors, however the instance I want to adjust is being able to refer to a variable say with the Exit Pupil rather than reusing the Mag formula, there are many instances where I have reused the same formulas multiple times, if I can set some of the equations to a variable it will significantly reduce the size and unnecessary complexities. Is there a way I can do this?

Answer 1

I suppose what you ask about recalculating can be done with With or other `scoping construct.

Manipulate[
 With[{mag = FL/OL, minmag = AD/OP},
      Grid[
       MapAt[ NumberForm[N@#, {\[Infinity], 4}] &,
              {{"Gathering Power: ", (minmag)^2}, 
               {"Magnification: ", mag}, 
               {"Min Magnification: ", minmag},
               {"Exit Pupil: ", AD/mag}, 
               {"True FOV (No F/Stop): ", OF/mag}, 
               {"Max FOV: ", (31.7*180)/(Pi*FL)}, 
               {"Longest Useful FOV: ", mag FL/AD}}
            , {All, 2}]
        , ItemStyle -> {{Bold, Orange}}, Alignment -> {{Left, "."}}]
     ]
     , 
      {{AD, 130, "Aperature: "}, 60, 508, 1, Appearance -> "Labeled"}, 
      {{FL, 650, "Focal Length: "}, 480, 4064, 1, Appearance -> "Labeled"}, 
      {{OL, 32, "Occular Focal Length: "}, 1, 110, 1, Appearance -> "Labeled"}, 
      {{OF, 52, "Occular FOV: "}, 40, 72, 1, Appearance -> "Labeled"}, 
      {{OP, 7, "Observer's Pupil: "}, 4, 9, 1, Appearance -> "Labeled"}]

Answer 2

May be I am missing something but Manipulate is designed to automatically re-evaluate when one variable in its expression changes.

Manipulate[
N@Grid[{
  {"Magnification: f/c = ", f/c},
  {"Exit Pupil: a/m =", a/(f/c)},
  {"Longest Useful FOV: f/e =", f/(a/(f/c))}
  }],
 {{a, 130, "Aperature: "}, 60, 508, 1,Appearance -> "Labeled"}, 
 {{f, 650, "Focal Length: "}, 480, 4064, 1,Appearance -> "Labeled"}, 
 {{c, 32, "Occular Focal Length: "}, 1,110, 1, Appearance -> "Labeled"}
 ]