Hi. Construct lets you select from many expressions from any text entry field that accepts those, such as the 'Set speed' action.
In case you don't know about any of these, I'll describe the process below.
Also, even object selection gadgets can be right-clicked and 'Use expression' can be selected. This would be the action (copied as text from Construct) for doing what you mentioned, if the sprite were named 'Unit':
-> Unit: Set speed to Unit[RTS].Speed - 10
You can access that 'Unit[RTS].Speed' using the mouse by doing the following:
- click 'new action' in the event sheet
- double-click the sprite with RTS behavior (named 'Unit' in the above case)
- click the 'RTS' tab at the top
- double-click 'Set speed'
Here's where you can access a multitude of 'expressions' that Construct provides. You can either just type them into the text entry, or select them from the usual list, or a combination of those is usually the case. From here:
- double-click the sprite again in the object view at the bottom of the window. This brings up all of the expressions for it.
- select the 'RTS' tab as before to get those specific to that behavior
- double-click 'Get speed'
Now just type in ' - 10' to the end of it.
The System object also has many useful expressions to use in such a way.