Sun DSS-10 smoke meter

i haven't got one of those, but i think its a case of keeping the lenses clean, especially in cold weather, as you get a lot of condensation forming due to warm exhaust gas/smoke and cold air.

You have a mean smoke level and a arithmetic mean which is calculated after 3 latest accelarations
If any of the last 3 readings is less then 75℅ of the "mean" smoke level ,that individual reading gets rejected and no mean value displayed .
What can cause that is lens dirty or,if the sample pipe is not fitted in accordance with the manufactures instructed it may prevent the DSM not receiving a pulse,engine not fully warmed up or machine has condensation .
Garages are cold and damp and we leave our ega and dsm switched on all of the time to keep it warm to prevent condensation through the winter months,condensation in these machines is a killer
When you get a reading of say 3.5 on acceleration then 0.1,then another 3.5 it normally ends up a void if you know what I mean
Just a couple of things you can try