Jorrie obviously doesn't have to adopt any of our suggestions in building his tabular (cosmic history) calculator. It's his project and he's doing all the work. But he's said in several threads that he would like reactions/suggestions from us (and he may have used them in some cases.) Maybe PF is a good environment for developing teach/learn tools like this. Maybe it would be constructive if people wanted to respond with whatever your thoughts are about his adding a 9th column about RECESSION SPEED history of a representative galaxy which today is at Hubble distance. 1. Should there be a 9th column at all? The table is getting fairly wide already. The calculator is intended to appeal to beginners so they can get familiar with standard model cosmology at a quantitative (not merely verbal) level. So one concern is not to overwhelm beginners with "too much all at once". 2. If there is to be a 9th column, should it be about recession speed? Have a look at the calculator. What would you like to see in the 9th column? What other kind of information could there be besides what is already in the first 8 columns? Here are the first 8, they seem essential to me. Do they to you? These are all things I would want to have handy and not be always having to calculate or go to Ned Wright's one-shot calculator for. Do you disagree? Would you reallocate any of the first 8 columns? stretch factor (i.e. redshift+1) scale factor Time Hubble radius at that time Distance now Distance then (at that time) cosmic event horizon at that time radius of observable region at that time (i.e. particle horizon) 3. Suppose a 9th column is adjoined to these and suppose it is going to be about the recession speed of some representative galaxy. What sample galaxy do you pick? What Jorrie is proposing, and has implemented already in his version 9 (link in his sig) is the sample galaxy should be one that today is at today's Hubble distance Rnow or Ro. That has the advantage that this distance Rnow is one of the 3 model parameters that are input to the model. (when you open the calculator you can either use the default Rnow=14 Gly or whatever, or you can type in some other parameter. It is part of the set-up. So that distance is "around". It serves as a kind of unit or reference scale. Should one be able to adjust this? Or should one keep it simple and just use Rnow? Should the column heading say "recession speed" e.g. vrec or should it say vrec/c because it is giving recession speed as a multiple of the speed of light or should it say Rnowda/dT, because that is what it is, mathematically (although that would not always say "recession speed" to every user)? Still undecided about some of this. Like to know your thoughts on it. Have to go, back soon.