CA Evid Code Section 354

A verdict or finding shall not be set aside, nor shall the judgment or decision based thereon be reversed, by reason of the erroneous exclusion of evidence unless the court which passes upon the effect of the error or errors is of the opinion that the error or errors complained of resulted in a miscarriage of justice and it appears of record that:

(a)

The substance, purpose, and relevance of the excluded evidence was made known to the court by the questions asked, an offer of proof, or by any other means;

(b)

The rulings of the court made compliance with subdivision (a) futile; or

(c)

The evidence was sought by questions asked during cross-examination or recross-examination.