Why not. . . ? LSS then comp?
Why not just calc Machno to get your TAS, then convert your TAS to EAS using your whizzwheel computor. . ?
The formula for Machnumber, as you know is (grab a calculator - its sssooooo easy)
the sqrt of 273 (+/- T) x 38.94
So stab in 273 add or subtract you outside temperatur (+/-T)
sq rt the result
then times it by 38.94 (you van prob do it by calculas too . . . but I really don`t wanna know, ok?)
then - you will have a number whic is you True Airspeed, ok?
Now, take this True Airspeed and using your metal or plastic flight computor you can calculate the EAS from the Tas.
Happy?