Algodoo

Well, since you mentioned accuracy, here are my thoughts:
  1. Friction between the side guides and the plate will affect the measurement.
  2. The person's head leaning against the side plate will affect the measurement.
  3. Buoyancy will affect the measurement.
  4. sim.frequency will affect the measurement (higher frequencies are typically more
   accurate).
  5. The side plates are not necessary.
  6. Weight is measured in Newtons.
  7. Mass is measured in kilograms.
  8. If you select the whole body, right click, then select information, then the total mass will
   be displayed.
  9. A more accurate value may be obtained by averaging many values.

Suggested formulas:
  Scene.my.mass = _Self.totImp3(1) * sim.frequency / Sim.gravityStrength - massOfPlate
  Scene.my.weight = _Self.totImp3(1) * sim.frequency - massOfPlate * Sim.gravityStrength

Here's some smoothing code:
  _massOfPlate := 2.0;
  _smoothedReading = 1.32;
  _TC = 2.0;  
      
  postStep = (e)=>{
    v := _Self.totImp3(1) * sim.frequency / Sim.gravityStrength - _massOfPlate;
    _smoothedReading = _smoothedReading + (v - _smoothedReading) / (sim.frequency * _TC);
    Scene.my.mass = _smoothedReading
  }

Display box code:
  text = math.toInt(Scene.my.mass * 1000000) * 1e-006 + " kilograms"

Results:
  The value that I get at sim.frequency = 300 Hz is 1.32746 kg which is within 0.03% of Algodoo's value of 1.327.

oh ok

I adore your work, i want to be just like you!