Taking a look inside 3 Martin Authentics and measuring top thickness. A 1963 Martin D-21 as a bonus.
(00:00) D-45S 1936 Authentic
(00:55) D-45 1942 Authentic
(01:44) D-28 1941 Authentic
(02:46) CS-Bluegrass-16
(03:52) 1963 D-21
(04:48) Using the MAG-ic Probe
(13:02) Top thickness data