U

U is an internal Universa measurement unit of energy required to execute some Universa transaction, i.e. to register some smart contracts/contract revisions.

The simplest and lightest transactions usually take just 1 U to be registered, more complex ones may require more. The details of calculation how much Us some transaction requires, are rather complex and low-level (you can find them at Quantization article in the Software Developer Central); but most of the times you just need to top-up your U balance (“reserve some U”) using UTN tokens.

Typically, the price of 1 U is around €0.01.

U smart contract:

1. is not a token; not intended to be used for any payment means. It cannot even be combined with other U token, cannot be “sent out” – the only supported method of operation is spending (i.e. decreasing the amount), not sending.
2. does not even supports changing the owner. The other reason why you cannot send it to someone and use it as a token, is that the owner of U smart contract is fixed at the moment of receiving the U contracts.
3. is time-limited. At the time of writing the article (early 2019), the lifetime of any issued U contract is set to 1 year. After 1 year passed since issuing the contract, you should expect the contract becoming invalid and REVOKED/UNDEFINED.

See also:

• U stock in Web Client, and how to top-up it.