Commodity is something which doesn’t have value without unit of measurement.
Examples of commodities are Helium, Gold, Silver, etc. All of these need
an unit of measurement to make transaction record sensible
bar for Helium or
oz for Gold).
Typically it is possible to transform commodity transactions between same commodity, but with different unit of measurement as long as there is well defined, constant conversion between those units.
42 Au oz →
1306.3460256 Au g →
1.3063460256 Au kg.
However, at the moment automatic commodity unit conversions are not supported with Tackler, but this is something which will be implemented in the future.
Commodity name (and combined unit) has to be a valid
ID element (same rules applies as with account names).
For example, tracking Helium and Oxygen, you could use units
Gas:Tank·102 298 He·bar Gas:Tank·208 195 O2·bar
if your tank sizes are known and fixed.
Transactions with mixed commodities
Transactions with mixed commodities without value positions are not allowed.
Example of invalid mixed commodity transaction without value positions:
2017-05-01 'This is invalid Vault:Bullion 1 Au·g Vault:Bullion 4 Ag·g Assets:Cash
Mixed commodities must be converted to common commodity with value positions:
2017-05-01 'This is valid Vault:Bullion 1 Au·g @ 37.00 EUR Vault:Bullion 1 Ag·g @ 0.495 EUR Assets:Cash
About He·bar and O2·bar
Strictly speaking it doesn’t make sense to track gas pressures, because you have to also know tank size to figure out actual amount of gas.
So original example of He and O2 tanks could be written in following way:
2019-04-01 'Gas amount in liters Gas:Tank·102 298 He·bar @ 50 He·l Gas:Tank·208 195 O2·bar @ 50 O2·l
assuming that 50 liter storage tanks are used.
For example see an accounting example for scuba diving Trimix Filling and Mixing Station. It demonstrates how to track different commodities and how to convert those commodities to monetary values.