Sterling ProCombiS Pure Sinewave Combination Charger Inverters There are 2 main models the Pro Combi Q for quasi-sinewave) and the Pro Combi S (for Pure-sinewave). So the simple question is what best suits your needs? Pro Combi Q, (quasi-sine model) suitable for most installations, where you would use a microwave, fridge, hair dryer, vacuum cleaner, kettle, computer, etc The vast majority of products will run on quasi-sinewave. Pro Combi S ( sine wave model ) where all the above plus washing machines, bread makers , thyristor controlled equipment are used - then sinewave is required