# Incorrect Calculation Logic
***
## Issue from Incorrect priceMarkUp Range
When using `priceMarkup`, it's important to carefully consider who bears the cost of any discount. Be mindful of scenarios where other users or the paymaster may be unfairly burdened.
Example Case:
If the `priceMarkUp` is too low (discount), only certain users may benefit from the reduced gas fees, while other users may be unable to access the amount they have deposited.
* Mitigation: The range of `priceMarkUp` should be restricted to ensure it does not negatively impact the protocol.
{% code overflow="wrap" %}
```solidity
require(_tokenPaymasterConfig.priceMarkup <= 2 * PRICE_DENOMINATOR, "TPM: price markup too high");
require(_tokenPaymasterConfig.priceMarkup >= PRICE_DENOMINATOR, "TPM: price markup too low");
```
{% endcode %}
***
## Overflow/Underflow Risk with Unchecked Operations
When using `unchecked` blocks to save gas, be cautious of overflow/underflow risks, especially when performing calculations with sensitive variables or user-supplied parameters.
Example Case:
If a user `withdraws` all their `deposit` while their `userOperation` is waiting in the mempool after the first validation, an underflow could occur in the gas payment process due to an `unchecked` code block.
Following this process, the user’s `deposit` approaches the maximum value, allowing them to potentially `withdraw` all of the Paymaster’s funds.
* Mitigation: A conditional statement should be used to compare the two values before performing the actual calculation to ensure that such issues do not occur.
```solidity
if (requiredGasCost > deposits[user]){
revert("deposit too low");
}
```
