Logic to list conversion rates

Where are stored conversion rates? Are they automatically created?

Looking at https://en.numista.com/catalogue/index.php?r=&st=all&cat=y&im1=&im2=&ru=&ie=&ca=3&no=&v=denaro&a=&dg=&i=&b=&m=&f=&t=&t2=&w=&mt=&u=&g=&c=&wi=&sw= 

I can see different logics for the same values

1 Lira = 20 Soldi = 60 Grossi = 240 Denari

12 Denari = 1 Soldo • 20 Soldi = 1 Lira

12 Denari = 1 Soldo • 20 Soldi = 10 Grossi = 1 Lira • 6 Lire = 1 Scudo

lira = 12 soldi = 240 denari

240 denari = 20 soldi = 1 lira

240 denari imperiali = 1 lira; 2 denari pavesi (mezzani) = 1 denaro imperiale

guidelines exist?

As the non-uniformity indicates they are in fact not created automatically but were/are added manually to the site by admins and now also translators.
But what is your suggestion you just posted a question?

Any interest in uniforming them? guidelines exist? Highest value first or lowest value first? Huge equation or single conversion rates divided by ; or - ?

https://en.numista.com/help/add-or-modify-a-currency-in-the-catalogue-194.html 

https://en.numista.com/help/add-or-modify-a-denomination-in-the-catalogue-206.html

Maybe the admins who actually add new ones have more precise guidelines?

This seems quite clear 

When known, the relative value of the subunits and super units is described in reference to the main currency unit. The main unit is used to specify the face values in figure form of all items within that currency:

• 1 Denarius = 2 Silver Quinarii = 4 Sestertii = 8 Dupondii = 16 Asses = 32 Semisses = 64 Quadrantes • 1 Aureus = 2 Gold Quinarii = 25 Denarii

1 Lira = 20 Soldi = 60 Grossi = 240 Denari

Right format

12 Denari = 1 Soldo • 20 Soldi = 1 Lira

should be changed to

1 Lira = 20 Soldi = 240 Denari

12 Denari = 1 Soldo • 20 Soldi = 10 Grossi = 1 Lira • 6 Lire = 1 Scudo

should be changed to

1 Scudo = 6 Lire = 60 Grossi = 120 Soldi = 1440 Denari

 lira = 12 soldi = 240 denari

seems wrong and should ne changed to

1 Lira = 20 Soldi = 240 Denari

240 denari = 20 soldi = 1 lira

should be changed to

 1 Lira = 20 Soldi = 240 Denari

240 denari imperiali = 1 lira; 2 denari pavesi (mezzani) = 1 denaro imperiale

 should be changed to

1 Lira = 240 Denari imperiali = 480 denari pavesi (mezzani)

When I translate conversion rates into Spanish, I request fix the orden in English (and other languages), but it is true there are many that are not fixed.

Alternatively, anyone can request a correction on the forum, posting a request about currencies and denominations.

@cippirimerlo  if you post a list of the ones you see, we can change them.

You are correct that the main (largest) unit comes first, so we should standardize on 

1 Lira = 20 Soldi = 240 Denari 

The grosso was not fixed in relation to the soldo or denaro in most places, and should not be in the list of equivalents.