Anyone get skew correction to compile (1 reply)

Marlin 1.1.9 with Folgertech i3 2020

I'm trying to understand how to implement skew correction. If I understand the comments in configuration.h I can either enter my measurements for XY_DIAG_AC, etc OR define XY_SKEW_FACTOR.
It seems that XY_SKEW_FACTOR overrides my enter measurements but if I comment out XY_SKEW_FACTOR I get a compile error.

#if ENABLED(SKEW_CORRECTION)
// Input all length measurements here:
// #define XY_DIAG_AC 282.8427124746
// #define XY_DIAG_BD 282.8427124746
// #define XY_SIDE_AD 200
#define XY_DIAG_AC 141,1 //08/19/18
#define XY_DIAG_BD 141.6
#define XY_SIDE_AD 100.6

// Or, set the default skew factors directly here
// to override the above measurements:
#define XY_SKEW_FACTOR 0.0

If I leave XY_SKEW_FACTOR defined when I do M852 I get all zeros and the print doesn't change.
I can put some value in XY_SKEW_FACTOR and it does get displayed via M852. Haven't tried another print.
I assume I'm doing something wrong but don't understand the comments.