1. Set store value to blank
By enabling the toggle icon, it will automatically set the store value to blank when the value in the feed file is blank as there is no value set in Compare-at Price section (zero or '0' are not considered as blank).
The feed file value must be empty so that it is able to become empty in the store.
2. Compare-at Price Round
Also available in Compare-at Price field but recommended to use the price round on the Price field as Default. 
You can click on the link here to learn more about the detail of the Price Round.
3. Currency Converter
You can also convert the currency in the Compare at Price field. You can enable the toggle to select the currency you want to apply.
4. Compare-at Price Condition (Markup)
Compare-at Price Condition is an extra setting under the Compare-at Price field. There are many conditions that can be applied through these settings. For more info about Compare-at Price condition.
In order to display the compare-at price in the store front, the compare-at price value must be higher than the price. For further information, please refer here.The Price Conditions take effect according to the arrangement. The first conditions have the highest priority.
Stock Sync also supports Column Value.
Valid price range keywords are:
- price
- any
- current_price
- cost
The symbol that is used for the statement:
- == equal to
- <= less than or equal to
- => more than or equal to
- and
- or