Gamma analysis, a procedure for tuning cyclic sediments in which gamma is defined as l/sedimentation rate, was applied to the upper Pleistocene gray scale record of Deep Sea Drilling Project site 609 from the North Atlantic. The spectrum of the gamma-tuned time series produces eccentricity, obliquity, and precession index signals when the primary periodicity is tuned to the precessional beat frequency. However, the timescales are significantly too long, suggesting that some of the primary cycles used in the gamma tuning procedure have higher frequency than the precessional beat. By filtering the SPECMAP-calibrated time series at 10--12 kyr the spurious cycles are removed from the tuning procedure. In this case, the resulting gamma-corrected spectra look much more like that of the SPECMAP-tuned time series. However, the time series remains slightly too long. Forward modeling is consistent with the results from modeling the core. That is, the gamma method is quite robust at revealing orbital periodicity in an orbitally controlled record for which sedimentation rates are facies dependent. However, the method does not produce an accurate time series. Criteria for complete rejection of gamma results are clarified as either (1) least squares results include negative gamma values or (2) the resulting spectrum does not show an orbital signature. Variation on sedimentation rates greater than ¿5% result in incorrect time series. However, variations on sedimentation rates as high as ¿15% generally reproduce strong orbital spectra, and occasionally, the method can also generate an orbital spectrum with up to ¿25% noise. The method is not as robust in predicting gamma values or sedimentation rates. Although it generally distinguishes facies with relatively high sedimentation rates from facies with relatively low sedimentation rates, the values predicted may be incorrect by a factor of 2. Thus while gamma tuning of the time series is an improvement over observed thicknesses, the resulting timescale is not correct. The implications of these results for cyclostratigraphy are significant. The generation of an orbital spectrum from a time series that is demonstrably incorrect casts doubt on cyclicity as a dating tool. ¿ American Geophysical Union 1996