In a decentralized network, misuse of the protocol is not direclty accountable so execution of smart contracts in an adversarial manner should be bounded economically. Following Ethereums GAS model, the QAN VM is also metered. Prices for opcodes are denominated in Spice, and follows the same economical incentives as the GAS model.
The actual settlement of spice for a contract call however, is calculated in Fiat currency. This happens trough ChainLink which is an oracle service feeding the current fiat price of QARK tokens back into the network. This way smartcontract owners can calculate and plan ahead of infrastructural costs for decenralized applications without being exposed to the volatility of the tokens price.
For example, a contract call
add which hypothetically costs 100 Spice, with a $1/QARK price and 1QARK/spice would cost $100 to call today. If the USD price of QARK jumps up to $2/QARK tomorrow, the network will still only subtract $100USD worth of QARKS from the caller wallet by using a 0.5QARK/spice value that we got from the 0x00000..1 precompile containing ChainLink data.