This is the top of the line in the Keuffel & Esser slide rules: 
the DECI-LON 10 - Serial number 098448 Model number 68-1100. 

K+E exclusive shatterproof synthetic celluloid construction. 12 1/2"+ long, 2"wide. Front scales: Sq1, Sq2, DF, CF, ClF , L, Cl, C, D, Ln0, Ln1, Ln2, Ln3. Reverse scales: Ln-3, Ln-2, Ln-1, Ln-0, A, B, T, SRT, S, C, D, Dl and K. 

Included is the trademark orange hard leather case with clip on strap; gold embossed "K+E" and "DECI-LON 10" logos.

Keuffel & Esser DECI-LON Slide Rule 1960s